NAME¶
snit - Snit's Not Incr Tcl
SYNOPSIS¶
package require
Tcl 8.5
package require
snit ?2.3.2?
snit::type name definition
typevariable name ?
-array? ?
value?
typemethod name arglist body
typeconstructor body
variable name ?
-array? ?
value?
method name arglist body
option namespec ?
defaultValue?
option namespec ?
options...?
constructor arglist body
destructor body
proc name args body
delegate method name to comp ?
as
target?
delegate method name ?
to comp?
using
pattern
delegate method * ?
to comp? ?
using
pattern? ?
except exceptions?
delegate option namespec to comp
delegate option namespec to comp as
target
delegate option * to comp
delegate option * to comp except
exceptions
component comp ?
-public method? ?
-inherit
flag?
delegate typemethod name to comp ?
as
target?
delegate typemethod name ?
to comp?
using pattern
delegate typemethod * ?
to comp? ?
using
pattern? ?
except exceptions?
typecomponent comp ?
-public typemethod?
?
-inherit flag?
pragma ?
options...?
expose comp
expose comp as method
onconfigure name arglist body
oncget name body
snit::widget name definition
widgetclass name
hulltype type
snit::widgetadaptor name definition
snit::typemethod type name arglist body
snit::method type name arglist body
snit::macro name arglist body
snit::compile which type body
$type typemethod args...
$type create name ?
option value ...?
$type info typevars ?
pattern?
$type info typemethods ?
pattern?
$type info args method
$type info body method
$type info default method aname varname
$type info instances ?
pattern?
$type destroy
$object method args...
$object configure ?
option? ?
value? ...
$object configurelist optionlist
$object cget option
$object destroy
$object info type
$object info vars ?
pattern?
$object info typevars ?
pattern?
$object info typemethods ?
pattern?
$object info options ?
pattern?
$object info methods ?
pattern?
$object info args method
$object info body method
$object info default method aname varname
mymethod name ?
args...?
mytypemethod name ?
args...?
myproc name ?
args...?
myvar name
mytypevar name
from argvName option ?
defvalue?
install compName using objType objName
args...
installhull using widgetType args...
installhull name
variable name
typevariable name
varname name
typevarname name
codename name
snit::boolean validate ?
value?
snit::boolean name
snit::double validate ?
value?
snit::double name ?
option value...?
snit::enum validate ?
value?
snit::enum name ?
option value...?
snit::fpixels validate ?
value?
snit::fpixels name ?
option value...?
snit::integer validate ?
value?
snit::integer name ?
option value...?
snit::listtype validate ?
value?
snit::listtype name ?
option value...?
snit::pixels validate ?
value?
snit::pixels name ?
option value...?
snit::stringtype validate ?
value?
snit::stringtype name ?
option value...?
snit::window validate ?
value?
snit::window name
DESCRIPTION¶
Snit is a pure Tcl object and megawidget system. It's unique among Tcl object
systems in that it's based not on inheritance but on delegation. Object
systems based on inheritance only allow you to inherit from classes defined
using the same system, which is limiting. In Tcl, an object is anything that
acts like an object; it shouldn't matter how the object was implemented. Snit
is intended to help you build applications out of the materials at hand; thus,
Snit is designed to be able to incorporate and build on any object, whether
it's a hand-coded object, a
Tk widget, an
Incr Tcl object, a
BWidget or almost anything else.
This man page is intended to be a reference only; see the accompanying
snitfaq for a gentler, more tutorial introduction to Snit concepts.
SNIT VERSIONS¶
This man page covers both Snit 2.2 and Snit 1.3. The primary difference between
the two versions is simply that Snit 2.2 contains speed optimizations based on
new features of Tcl 8.5; Snit 1.3 supports all of Tcl 8.3, 8.4 and Tcl 8.5.
There are a few minor inconsistencies; they are flagged in the body of the man
page with the label "Snit 1.x Incompatibility"; they are also
discussed in the
snitfaq.
REFERENCE¶
Snit provides the following commands for defining new types:
- snit::type name definition
- Defines a new abstract data type called name. If name is not
a fully qualified command name, it is assumed to be a name in the
namespace in which the snit::type command was called (usually the
global namespace). It returns the fully qualified name of the new type.
The type name is then a command that is used to create objects of the new
type, along with other activities.
The snit::type definition block is a script that may contain
the following definitions:
- typevariable name ?-array? ?value?
- Defines a type variable with the specified name, and optionally the
specified value. Type variables are shared by all instances of the
type. If the -array option is included, then value should be
a dictionary; it will be assigned to the variable using array
set.
- typemethod name arglist body
- Defines a type method, a subcommand of the new type command, with the
specified name, argument list, and body. The arglist is a normal
Tcl argument list and may contain default arguments and the args
argument; however, it may not contain the argument names type,
self, selfns, or win.
The variable type is automatically defined in the body to the
type's fully-qualified name. In addition, type variables are automatically
visible in the body of every type method.
If the name consists of two or more tokens, Snit handles it
specially:
typemethod {a b} {arg} { puts "Got $arg" }
- This statement implicitly defines a type method called a which has
a subcommand b. b is called like this:
$type a b "Hello, world!"
- a may have any number of subcommands. This makes it possible to
define a hierarchical command structure; see method, below, for
more examples.
Type methods can call commands from the namespace in which the type is
defined without importing them, e.g., if the type name is
::parentns::typename, then the type's type methods can call
::parentns::someproc just as someproc. Snit 1.x
Incompatibility: This does not work in Snit 1.x, as it depends on
namespace path, a new command in Tcl 8.5.
Snit 1.x Incompatibility: In Snit 1.x, the following following two
calls to this type method are equivalent:
$type a b "Hello, world!"
$type {a b} "Hello, world!"
- In Snit 2.2, the second form is invalid.
- typeconstructor body
- The type constructor's body is executed once when the type is first
defined; it is typically used to initialize array-valued type variables
and to add entries to The Tk Option Database.
The variable type is automatically defined in the body, and
contains the type's fully-qualified name. In addition, type variables are
automatically visible in the body of the type constructor.
A type may define at most one type constructor.
The type constructor can call commands from the namespace in which the type
is defined without importing them, e.g., if the type name is
::parentns::typename, then the type constructor can call
::parentns::someproc just as someproc. Snit 1.x
Incompatibility: This does not work in Snit 1.x, as it depends on
namespace path, a new command in Tcl 8.5.
- variable name ?-array? ?value?
- Defines an instance variable, a private variable associated with each
instance of this type, and optionally its initial value. If the
-array option is included, then value should be a
dictionary; it will be assigned to the variable using array
set.
- method name arglist body
- Defines an instance method, a subcommand of each instance of this type,
with the specified name, argument list and body. The arglist is a
normal Tcl argument list and may contain default arguments and the
args argument.
The method is implicitly passed the following arguments as well:
type, which contains the fully-qualified type name; self,
which contains the current instance command name; selfns, which
contains the name of the instance's private namespace; and win,
which contains the original instance name. Consequently, the
arglist may not contain the argument names type,
self, selfns, or win.
An instance method defined in this way is said to be locally defined.
Type and instance variables are automatically visible in all instance
methods. If the type has locally defined options, the options array
is also visible.
If the name consists of two or more tokens, Snit handles it
specially:
- This statement implicitly defines a method called a which has a
subcommand b. b is called like this:
$self a b "Hello, world!"
- a may have any number of subcommands. This makes it possible to
define a hierarchical command structure:
% snit::type dog {
method {tail wag} {} {return "Wag, wag"}
method {tail droop} {} {return "Droop, droop"}
}
::dog
% dog spot
::spot
% spot tail wag
Wag, wag
% spot tail droop
Droop, droop
%
- What we've done is implicitly defined a "tail" method with
subcommands "wag" and "droop". Consequently, it's an
error to define "tail" explicitly.
Methods can call commands from the namespace in which the type is defined
without importing them, e.g., if the type name is
::parentns::typename, then the type's methods can call
::parentns::someproc just as someproc. Snit 1.x
Incompatibility: This does not work in Snit 1.x, as it depends on
namespace path, a new command in Tcl 8.5.
Snit 1.x Incompatibility: In Snit 1.x, the following following two
calls to this method are equivalent:
$self a b "Hello, world!"
$self {a b} "Hello, world!"
- In Snit 2.2, the second form is invalid.
- option namespec ?defaultValue?
- option namespec ?options...?
- Defines an option for instances of this type, and optionally gives it an
initial value. The initial value defaults to the empty string if no
defaultValue is specified.
An option defined in this way is said to be locally defined.
The namespec is a list defining the option's name, resource name, and
class name, e.g.:
option {-font font Font} {Courier 12}
- The option name must begin with a hyphen, and must not contain any upper
case letters. The resource name and class name are optional; if not
specified, the resource name defaults to the option name, minus the
hyphen, and the class name defaults to the resource name with the first
letter capitalized. Thus, the following statement is equivalent to the
previous example:
option -font {Courier 12}
- See The Tk Option Database for more information about resource and
class names.
Options are normally set and retrieved using the standard instance methods
configure and cget; within instance code (method bodies,
etc.), option values are available through the options array:
set myfont $options(-font)
- If the type defines any option handlers (e.g., -configuremethod),
then it should probably use configure and cget to access its
options to avoid subtle errors.
The option statement may include the following options:
- -default defvalue
- Defines the option's default value; the option's default value will be
"" otherwise.
- -readonly flag
- The flag can be any Boolean value recognized by Tcl. If flag
is true, then the option is read-only--it can only be set using
configure or configurelist at creation time, i.e., in the
type's constructor.
- -type type
- Every locally-defined option may define its validation type, which may be
either the name of a validation type or a specification for a validation
subtype
For example, an option may declare that its value must be an integer by
specifying snit::integer as its validation type:
option -number -type snit::integer
- It may also declare that its value is an integer between 1 and 10 by
specifying a validation subtype:
option -number -type {snit::integer -min 1 -max 10}
- If a validation type or subtype is defined for an option, then it will be
used to validate the option's value whenever it is changed by the object's
configure or configurelist methods. In addition, all such
options will have their values validated automatically immediately after
the constructor executes.
Snit defines a family of validation types and subtypes, and it's quite
simple to define new ones. See Validation Types for the complete
list, and Defining Validation Types for an explanation of how to
define your own.
- -cgetmethod methodName
- Every locally-defined option may define a -cgetmethod; it is called
when the option's value is retrieved using the cget method.
Whatever the method's body returns will be the return value of the
call to cget.
The named method must take one argument, the option name. For example, this
code is equivalent to (though slower than) Snit's default handling of
cget:
option -font -cgetmethod GetOption
method GetOption {option} {
return $options($option)
}
- Note that it's possible for any number of options to share a
-cgetmethod.
- -configuremethod methodName
- Every locally-defined option may define a -configuremethod; it is
called when the option's value is set using the configure or
configurelist methods. It is the named method's responsibility to
save the option's value; in other words, the value will not be saved to
the options() array unless the method saves it there.
The named method must take two arguments, the option name and its new value.
For example, this code is equivalent to (though slower than) Snit's
default handling of configure:
option -font -configuremethod SetOption
method SetOption {option value} {
set options($option) $value
}
- Note that it's possible for any number of options to share a single
-configuremethod.
- -validatemethod methodName
- Every locally-defined option may define a -validatemethod; it is
called when the option's value is set using the configure or
configurelist methods, just before the -configuremethod (if
any). It is the named method's responsibility to validate the option's new
value, and to throw an error if the value is invalid.
The named method must take two arguments, the option name and its new value.
For example, this code verifies that -flag's value is a valid
Boolean value:
option -font -validatemethod CheckBoolean
method CheckBoolean {option value} {
if {![string is boolean -strict $value]} {
error "option $option must have a boolean value."
}
}
- Note that it's possible for any number of options to share a single
-validatemethod.
- constructor arglist body
- The constructor definition specifies a body of code to be executed
when a new instance is created. The arglist is a normal Tcl
argument list and may contain default arguments and the args
argument.
As with methods, the arguments type, self, selfns, and
win are defined implicitly, and all type and instance variables are
automatically visible in its body.
If the definition doesn't explicitly define the constructor, Snit
defines one implicitly. If the type declares at least one option (whether
locally or by delegation), the default constructor will be defined as
follows:
constructor {args} {
$self configurelist $args
}
- For standard Tk widget behavior, the argument list should be the single
name args, as shown.
If the definition defines neither a constructor nor any options, the
default constructor is defined as follows:
- As with methods, the constructor can call commands from the namespace in
which the type is defined without importing them, e.g., if the type name
is ::parentns::typename, then the constructor can call
::parentns::someproc just as someproc. Snit 1.x
Incompatibility: This does not work in Snit 1.x, as it depends on
namespace path, a new command in Tcl 8.5.
- destructor body
- The destructor is used to code any actions that must take place when an
instance of the type is destroyed: typically, the destruction of anything
created in the constructor.
The destructor takes no explicit arguments; as with methods, the arguments
type, self, selfns, and win, are defined
implicitly, and all type and instance variables are automatically visible
in its body. As with methods, the destructor can call commands from
the namespace in which the type is defined without importing them, e.g.,
if the type name is ::parentns::typename, then the destructor can
call ::parentns::someproc just as someproc. Snit 1.x
Incompatibility: This does not work in Snit 1.x, as it depends on
namespace path, a new command in Tcl 8.5.
- proc name args body
- Defines a new Tcl procedure in the type's namespace.
The defined proc differs from a normal Tcl proc in that all type variables
are automatically visible. The proc can access instance variables as well,
provided that it is passed selfns (with precisely that name) as one
of its arguments.
Although they are not implicitly defined for procs, the argument names
type, self, and win should be avoided.
As with methods and typemethods, procs can call commands from the namespace
in which the type is defined without importing them, e.g., if the type
name is ::parentns::typename, then the proc can call
::parentns::someproc just as someproc. Snit 1.x
Incompatibility: This does not work in Snit 1.x, as it depends on
namespace path, a new command in Tcl 8.5.
- delegate method name to comp ?as
target?
- Delegates method name to component comp. That is, when
method name is called on an instance of this type, the method and
its arguments will be passed to the named component's command instead.
That is, the following statement
delegate method wag to tail
- is roughly equivalent to this explicitly defined method:
method wag {args} {
uplevel $tail wag $args
}
- As with methods, the name may have multiple tokens; in this case,
the last token of the name is assumed to be the name of the component's
method.
The optional as clause allows you to specify the delegated method
name and possibly add some arguments:
delegate method wagtail to tail as "wag briskly"
A method cannot be both locally defined and delegated.
Note: All forms of
delegate method can delegate to both instance
components and type components.
- delegate method name ?to comp?
using pattern
- In this form of the delegate statement, the using clause is
used to specify the precise form of the command to which method
name name is delegated. In this form, the to clause is
optional, since the chosen command might not involve any particular
component.
The value of the using clause is a list that may contain any or all
of the following substitution codes; these codes are substituted with the
described value to build the delegated command prefix. Note that the
following two statements are equivalent:
delegate method wag to tail
delegate method wag to tail using "%c %m"
- Each element of the list becomes a single element of the delegated
command--it is never reparsed as a string.
Substitutions:
- %%
- This is replaced with a single "%". Thus, to pass the string
"%c" to the command as an argument, you'd write
"%%c".
- %c
- This is replaced with the named component's command.
- %m
- This is replaced with the final token of the method name; if the
method name has one token, this is identical to %M.
- %M
- This is replaced by the method name; if the name consists of
multiple tokens, they are joined by space characters.
- %j
- This is replaced by the method name; if the name consists of
multiple tokens, they are joined by underscores ("_").
- %t
- This is replaced with the fully qualified type name.
- %n
- This is replaced with the name of the instance's private namespace.
- %s
- This is replaced with the name of the instance command.
- %w
- This is replaced with the original name of the instance command; for Snit
widgets and widget adaptors, it will be the Tk window name. It remains
constant, even if the instance command is renamed.
- delegate method * ?to comp?
?using pattern? ?except exceptions?
- The form delegate method * delegates all unknown method names to
the specified component. The except clause can be used to
specify a list of exceptions, i.e., method names that will not be
so delegated. The using clause is defined as given above. In this
form, the statement must contain the to clause, the using
clause, or both.
In fact, the "*" can be a list of two or more tokens whose last
element is "*", as in the following example:
delegate method {tail *} to tail
- This implicitly defines the method tail whose subcommands will be
delegated to the tail component.
- delegate option namespec to comp
- delegate option namespec to comp
as target
- delegate option * to comp
- delegate option * to comp except
exceptions
- Defines a delegated option; the namespec is defined as for the
option statement. When the configure, configurelist,
or cget instance method is used to set or retrieve the option's
value, the equivalent configure or cget command will be
applied to the component as though the option was defined with the
following -configuremethod and -cgetmethod:
method ConfigureMethod {option value} {
$comp configure $option $value
}
method CgetMethod {option} {
return [$comp cget $option]
}
- Note that delegated options never appear in the options array.
If the as clause is specified, then the target option name is
used in place of name.
The form delegate option * delegates all unknown options to the
specified component. The except clause can be used to
specify a list of exceptions, i.e., option names that will not be
so delegated.
Warning: options can only be delegated to a component if it supports the
configure and cget instance methods.
An option cannot be both locally defined and delegated. TBD: Continue from
here.
- component comp ?-public method?
?-inherit flag?
- Explicitly declares a component called comp, and automatically
defines the component's instance variable.
If the -public option is specified, then the option is made public by
defining a method whose subcommands are delegated to the component
e.g., specifying -public mycomp is equivalent to the
following:
component mycomp
delegate method {mymethod *} to mycomp
- If the -inherit option is specified, then flag must be a
Boolean value; if flag is true then all unknown methods and options
will be delegated to this component. The name -inherit implies that
instances of this new type inherit, in a sense, the methods and options of
the component. That is, -inherit yes is equivalent to:
component mycomp
delegate option * to mycomp
delegate method * to mycomp
- delegate typemethod name to comp
?as target?
- Delegates type method name to type component comp. That is,
when type method name is called on this type, the type method and
its arguments will be passed to the named type component's command
instead. That is, the following statement
delegate typemethod lostdogs to pound
- is roughly equivalent to this explicitly defined method:
typemethod lostdogs {args} {
uplevel $pound lostdogs $args
}
- As with type methods, the name may have multiple tokens; in this
case, the last token of the name is assumed to be the name of the
component's method.
The optional as clause allows you to specify the delegated method
name and possibly add some arguments:
delegate typemethod lostdogs to pound as "get lostdogs"
A type method cannot be both locally defined and delegated.
- delegate typemethod name ?to comp?
using pattern
- In this form of the delegate statement, the using clause is
used to specify the precise form of the command to which type method
name name is delegated. In this form, the to clause is
optional, since the chosen command might not involve any particular type
component.
The value of the using clause is a list that may contain any or all
of the following substitution codes; these codes are substituted with the
described value to build the delegated command prefix. Note that the
following two statements are equivalent:
delegate typemethod lostdogs to pound
delegate typemethod lostdogs to pound using "%c %m"
- Each element of the list becomes a single element of the delegated
command--it is never reparsed as a string.
Substitutions:
- %%
- This is replaced with a single "%". Thus, to pass the string
"%c" to the command as an argument, you'd write
"%%c".
- %c
- This is replaced with the named type component's command.
- %m
- This is replaced with the final token of the type method name; if
the type method name has one token, this is identical to
%M.
- %M
- This is replaced by the type method name; if the name
consists of multiple tokens, they are joined by space characters.
- %j
- This is replaced by the type method name; if the name
consists of multiple tokens, they are joined by underscores
("_").
- %t
- This is replaced with the fully qualified type name.
- delegate typemethod * ?to comp?
?using pattern? ?except exceptions?
- The form delegate typemethod * delegates all unknown type method
names to the specified type component. The except clause can be
used to specify a list of exceptions, i.e., type method names that
will not be so delegated. The using clause is defined as given
above. In this form, the statement must contain the to clause, the
using clause, or both.
Note: By default, Snit interprets $type foo, where foo
is not a defined type method, as equivalent to $type create foo,
where foo is the name of a new instance of the type. If you use
delegate typemethod *, then the create type method must
always be used explicitly.
The "*" can be a list of two or more tokens whose last element is
"*", as in the following example:
delegate typemethod {tail *} to tail
- This implicitly defines the type method tail whose subcommands will
be delegated to the tail type component.
- typecomponent comp ?-public typemethod?
?-inherit flag?
- Explicitly declares a type component called comp, and automatically
defines the component's type variable. A type component is an arbitrary
command to which type methods and instance methods can be delegated; the
command's name is stored in a type variable.
If the -public option is specified, then the type component is made
public by defining a typemethod whose subcommands are delegated to
the type component, e.g., specifying -public mytypemethod is
equivalent to the following:
typecomponent mycomp
delegate typemethod {mytypemethod *} to mycomp
- If the -inherit option is specified, then flag must be a
Boolean value; if flag is true then all unknown type methods will
be delegated to this type component. (See the note on "delegate
typemethod *", above.) The name -inherit implies that this
type inherits, in a sense, the behavior of the type component. That is,
-inherit yes is equivalent to:
typecomponent mycomp
delegate typemethod * to mycomp
- pragma ?options...?
- The pragma statement provides control over how Snit generates a
type. It takes the following options; in each case, flag must be a
Boolean value recognized by Tcl, e.g., 0, 1, yes,
no, and so on.
By setting the -hastypeinfo, -hastypedestroy, and
-hasinstances pragmas to false and defining appropriate type
methods, you can create an ensemble command without any extraneous
behavior.
- -canreplace flag
- If false (the default) Snit will not create an instance of a
snit::type that has the same name as an existing command; this
prevents subtle errors. Setting this pragma to true restores the behavior
of Snit V0.93 and earlier versions.
- -hastypeinfo flag
- If true (the default), the generated type will have a type method called
info that is used for type introspection; the info type
method is documented below. If false, it will not.
- -hastypedestroy flag
- If true (the default), the generated type will have a type method called
destroy that is used to destroy the type and all of its instances.
The destroy type method is documented below. If false, it will
not.
- -hastypemethods flag
- If true (the default), the generated type's type command will have
subcommands (type methods) as usual. If false, the type command will serve
only to create instances of the type; the first argument is the instance
name.
This pragma and -hasinstances cannot both be set false.
- -hasinstances flag
- If true (the default), the generated type will have a type method called
create that is used to create instances of the type, along with a
variety of instance-related features. If false, it will not.
This pragma and -hastypemethods cannot both be set false.
- -hasinfo flag
- If true (the default), instances of the generated type will have an
instance method called info that is used for instance
introspection; the info method is documented below. If false, it
will not.
- -simpledispatch flag
- This pragma is intended to make simple, heavily-used abstract data types
(e.g., stacks and queues) more efficient.
If false (the default), instance methods are dispatched normally. If true, a
faster dispatching scheme is used instead. The speed comes at a price;
with -simpledispatch yes you get the following limitations:
- •
- Methods cannot be delegated.
- •
- uplevel and upvar do not work as expected: the caller's
scope is two levels up rather than one.
- •
- The option-handling methods ( cget, configure, and
configurelist) are very slightly slower.
- expose comp
- expose comp as method
- Deprecated. To expose component comp publicly, use
component's -public option.
- onconfigure name arglist body
- Deprecated. Define option's -configuremethod option
instead.
As of version 0.95, the following definitions,
option -myoption
onconfigure -myoption {value} {
# Code to save the option's value
}
- are implemented as follows:
option -myoption -configuremethod _configure-myoption
method _configure-myoption {_option value} {
# Code to save the option's value
}
- oncget name body
- Deprecated. Define option's -cgetmethod option
instead.
As of version 0.95, the following definitions,
option -myoption
oncget -myoption {
# Code to return the option's value
}
- are implemented as follows:
option -myoption -cgetmethod _cget-myoption
method _cget-myoption {_option} {
# Code to return the option's value
}
- snit::widget name definition
- This command defines a Snit megawidget type with the specified
name. The definition is defined as for snit::type. A
snit::widget differs from a snit::type in these ways:
- •
- Every instance of a snit::widget has an automatically-created
component called hull, which is normally a Tk frame widget. Other
widgets created as part of the megawidget will be created within this
widget.
The hull component is initially created with the requested widget name; then
Snit does some magic, renaming the hull component and installing its own
instance command in its place. The hull component's new name is saved in
an instance variable called hull.
- •
- The name of an instance must be valid Tk window name, and the parent
window must exist.
- A snit::widget definition can include any of statements allowed in
a snit::type definition, and may also include the following:
- widgetclass name
- Sets the snit::widget's widget class to name, overriding the
default. See The Tk Option Database for more information.
- hulltype type
- Determines the kind of widget used as the snit::widget's hull. The
type may be frame (the default), toplevel,
labelframe; the qualified equivalents of these, tk::frame,
tk::toplevel, and tk::labelframe; or, if available, the
equivalent Tile widgets: ttk::frame, ttk::toplevel, and
ttk::labelframe. In practice, any widget that supports the
-class option can be used as a hull widget by lappend'ing
its name to the variable snit::hulltypes.
- snit::widgetadaptor name definition
- This command defines a Snit megawidget type with the specified name. It
differs from snit::widget in that the instance's hull
component is not created automatically, but is created in the constructor
and installed using the installhull command. Once the hull is
installed, its instance command is renamed and replaced as with normal
snit::widgets. The original command is again accessible in the
instance variable hull.
Note that in general it is not possible to change the widget class of
a snit::widgetadaptor's hull widget.
See The Tk Option Database for information on how
snit::widgetadaptors interact with the option database.
- snit::typemethod type name arglist
body
- Defines a new type method (or redefines an existing type method) for a
previously existing type.
- snit::method type name arglist
body
- Defines a new instance method (or redefines an existing instance method)
for a previously existing type. Note that delegated instance
methods can't be redefined.
- snit::macro name arglist body
- Defines a Snit macro with the specified name, arglist, and
body. Macros are used to define new type and widget definition
statements in terms of the statements defined in this man page.
A macro is simply a Tcl proc that is defined in the slave interpreter used
to compile type and widget definitions. Thus, macros have access to all of
the type and widget definition statements. See Macros and
Meta-programming for more details.
The macro name cannot be the same as any standard Tcl command, or any
Snit type or widget definition statement, e.g., you can't redefine the
method or delegate statements, or the standard set,
list, or string commands.
- snit::compile which type body
- Snit defines a type, widget, or widgetadaptor by "compiling" the
definition into a Tcl script; this script is then evaluated in the Tcl
interpreter, which actually defines the new type.
This command exposes the "compiler". Given a definition
body for the named type, where which is type,
widget, or widgetadaptor, snit::compile returns a
list of two elements. The first element is the fully qualified type name;
the second element is the definition script.
snit::compile is useful when additional processing must be done on
the Snit-generated code--if it must be instrumented, for example, or run
through the TclDevKit compiler. In addition, the returned script could be
saved in a ".tcl" file and used to define the type as part of an
application or library, thus saving the compilation overhead at
application start-up. Note that the same version of Snit must be used at
run-time as at compile-time.
THE TYPE COMMAND¶
A type or widget definition creates a type command, which is used to create
instances of the type. The type command has this form:
- $type typemethod args...
- The typemethod can be any of the Standard Type Methods
(e.g., create), or any type method defined in the type definition.
The subsequent args depend on the specific typemethod
chosen.
The type command is most often used to create new instances of the type;
hence, the create method is assumed if the first argument to the
type command doesn't name a valid type method, unless the type definition
includes delegate typemethod * or the -hasinstances pragma
is set to false.
Furthermore, if the -hastypemethods pragma is false, then Snit type
commands can be called with no arguments at all; in this case, the type
command creates an instance with an automatically generated name. In other
words, provided that the -hastypemethods pragma is false and the
type has instances, the following commands are equivalent:
snit::type dog { ... }
set mydog [dog create %AUTO%]
set mydog [dog %AUTO%]
set mydog [dog]
- This doesn't work for Snit widgets, for obvious reasons.
Snit 1.x Incompatibility: In Snit 1.x, the above behavior is
available whether -hastypemethods is true (the default) or
false.
STANDARD TYPE METHODS¶
In addition to any type methods in the type's definition, all type and widget
commands will usually have at least the following subcommands:
- $type create name ?option value
...?
- Creates a new instance of the type, giving it the specified name
and calling the type's constructor.
For snit::types, if name is not a fully-qualified command
name, it is assumed to be a name in the namespace in which the call to
snit::type appears. The method returns the fully-qualified instance
name.
For snit::widgets and snit::widgetadaptors, name must
be a valid widget name; the method returns the widget name.
So long as name does not conflict with any defined type method name
the create keyword may be omitted, unless the type definition
includes delegate typemethod * or the -hasinstances pragma
is set to false.
If the name includes the string %AUTO%, it will be replaced
with the string $type$counter where $type is the type name
and $counter is a counter that increments each time %AUTO%
is used for this type.
By default, any arguments following the name will be a list of
option names and their values; however, a type's constructor
can specify a different argument list.
As of Snit V0.95, create will throw an error if the name is
the same as any existing command--note that this was always true for
snit::widgets and snit::widgetadaptors. You can restore the
previous behavior using the -canreplace pragma.
- $type info typevars ?pattern?
- Returns a list of the type's type variables (excluding Snit internal
variables); all variable names are fully-qualified.
If pattern is given, it's used as a string match pattern; only
names that match the pattern are returned.
- $type info typemethods ?pattern?
- Returns a list of the names of the type's type methods. If the type has
hierarchical type methods, whether locally-defined or delegated, only the
first word of each will be included in the list.
If the type definition includes delegate typemethod *, the list will
include only the names of those implicitly delegated type methods that
have been called at least once and are still in the type method cache.
If pattern is given, it's used as a string match pattern; only
names that match the pattern are returned.
- $type info args method
- Returns a list containing the names of the arguments to the type's
method, in order. This method cannot be applied to delegated type
methods.
- $type info body method
- Returns the body of typemethod method. This method cannot be
applied to delegated type methods.
- $type info default method aname
varname
- Returns a boolean value indicating whether the argument aname of
the type's method has a default value (true) or not (
false). If the argument has a default its value is placed into the
variable varname.
- $type info instances ?pattern?
- Returns a list of the type's instances. For snit::types, it will be
a list of fully-qualified instance names; for snit::widgets, it
will be a list of Tk widget names.
If pattern is given, it's used as a string match pattern; only
names that match the pattern are returned.
Snit 1.x Incompatibility: In Snit 1.x, the full multi-word names of
hierarchical type methods are included in the return value.
- $type destroy
- Destroys the type's instances, the type's namespace, and the type command
itself.
THE INSTANCE COMMAND¶
A Snit type or widget's
create type method creates objects of the type;
each object has a unique name that is also a Tcl command. This command is used
to access the object's methods and data, and has this form:
- $object method args...
- The method can be any of the Standard Instance Methods, or
any instance method defined in the type definition. The subsequent
args depend on the specific method chosen.
STANDARD INSTANCE METHODS¶
In addition to any delegated or locally-defined instance methods in the type's
definition, all Snit objects will have at least the following subcommands:
- $object configure ?option? ?value? ...
- Assigns new values to one or more options. If called with one argument, an
option name, returns a list describing the option, as Tk widgets
do; if called with no arguments, returns a list of lists describing all
options, as Tk widgets do.
Warning: This information will be available for delegated options only if
the component to which they are delegated has a configure method
that returns this same kind of information.
Note: Snit defines this method only if the type has at least one
option.
- $object configurelist optionlist
- Like configure, but takes one argument, a list of options and their
values. It's mostly useful in the type constructor, but can be used
anywhere.
Note: Snit defines this method only if the type has at least one
option.
- $object cget option
- Returns the option's value.
Note: Snit defines this method only if the type has at least one
option.
- $object destroy
- Destroys the object, calling the destructor and freeing all related
memory.
Note: The destroy method isn't defined for
snit::widget or snit::widgetadaptor objects; instances of
these are destroyed by calling Tk's destroy command, just as
normal widgets are.
- $object info type
- Returns the instance's type.
- $object info vars ?pattern?
- Returns a list of the object's instance variables (excluding Snit internal
variables). The names are fully qualified.
If pattern is given, it's used as a string match pattern; only
names that match the pattern are returned.
- $object info typevars ?pattern?
- Returns a list of the object's type's type variables (excluding Snit
internal variables). The names are fully qualified.
If pattern is given, it's used as a string match pattern; only
names that match the pattern are returned.
- $object info typemethods ?pattern?
- Returns a list of the names of the type's type methods. If the type has
hierarchical type methods, whether locally-defined or delegated, only the
first word of each will be included in the list.
If the type definition includes delegate typemethod *, the list will
include only the names of those implicitly delegated type methods that
have been called at least once and are still in the type method cache.
If pattern is given, it's used as a string match pattern; only
names that match the pattern are returned.
Snit 1.x Incompatibility: In Snit 1.x, the full multi-word names of
hierarchical type methods are included in the return value.
- $object info options ?pattern?
- Returns a list of the object's option names. This always includes local
options and explicitly delegated options. If unknown options are delegated
as well, and if the component to which they are delegated responds to
$object configure like Tk widgets do, then the result will include
all possible unknown options that can be delegated to the component.
If pattern is given, it's used as a string match pattern; only
names that match the pattern are returned.
Note that the return value might be different for different instances of the
same type, if component object types can vary from one instance to
another.
- $object info methods ?pattern?
- Returns a list of the names of the instance's methods. If the type has
hierarchical methods, whether locally-defined or delegated, only the first
word of each will be included in the list.
If the type definition includes delegate method *, the list will
include only the names of those implicitly delegated methods that have
been called at least once and are still in the method cache.
If pattern is given, it's used as a string match pattern; only
names that match the pattern are returned.
Snit 1.x Incompatibility: In Snit 1.x, the full multi-word names of
hierarchical type methods are included in the return value.
- $object info args method
- Returns a list containing the names of the arguments to the instance's
method, in order. This method cannot be applied to delegated
methods.
- $object info body method
- Returns the body of the instance's method method. This method
cannot be applied to delegated methods.
- $object info default method aname
varname
- Returns a boolean value indicating whether the argument aname of
the instance's method has a default value (true) or not (
false). If the argument has a default its value is placed into the
variable varname.
COMMANDS FOR USE IN OBJECT CODE¶
Snit defines the following commands for use in your object code: that is, for
use in type methods, instance methods, constructors, destructors, onconfigure
handlers, oncget handlers, and procs. They do not reside in the ::snit::
namespace; instead, they are created with the type, and can be used without
qualification.
- mymethod name ?args...?
- The mymethod command is used for formatting callback commands to be
passed to other objects. It returns a command that when called will invoke
method name with the specified arguments, plus of course any
arguments added by the caller. In other words, both of the following
commands will cause the object's dosomething method to be called
when the $button is pressed:
$button configure -command [list $self dosomething myargument]
$button configure -command [mymethod dosomething myargument]
- The chief distinction between the two is that the latter form will not
break if the object's command is renamed.
- mytypemethod name ?args...?
- The mytypemethod command is used for formatting callback commands
to be passed to other objects. It returns a command that when called will
invoke type method name with the specified arguments, plus of
course any arguments added by the caller. In other words, both of the
following commands will cause the object's dosomething type method
to be called when $button is pressed:
$button configure -command [list $type dosomething myargument]
$button configure -command [mytypemethod dosomething myargument]
- Type commands cannot be renamed, so in practice there's little difference
between the two forms. mytypemethod is provided for parallelism
with mymethod.
- myproc name ?args...?
- The myproc command is used for formatting callback commands to be
passed to other objects. It returns a command that when called will invoke
the type proc name with the specified arguments, plus of course any
arguments added by the caller. In other words, both of the following
commands will cause the object's dosomething proc to be called when
$button is pressed:
$button configure -command [list ${type}::dosomething myargument]
$button configure -command [myproc dosomething myargument]
- myvar name
- Given an instance variable name, returns the fully qualified name. Use
this if you're passing the variable to some other object, e.g., as a
-textvariable to a Tk label widget.
- mytypevar name
- Given an type variable name, returns the fully qualified name. Use this if
you're passing the variable to some other object, e.g., as a
-textvariable to a Tk label widget.
- from argvName option ?defvalue?
- The from command plucks an option value from a list of options and
their values, such as is passed into a type's constructor.
argvName must be the name of a variable containing such a list;
option is the name of the specific option.
from looks for option in the option list. If it is found, it
and its value are removed from the list, and the value is returned. If
option doesn't appear in the list, then the defvalue is
returned. If the option is locally-defined option, and defvalue is
not specified, then the option's default value as specified in the type
definition will be returned instead.
- install compName using objType objName
args...
- Creates a new object of type objType called objName and
installs it as component compName, as described in Components
and Delegation. Any additional args... are passed along with
the name to the objType command. If this is a snit::type,
then the following two commands are equivalent:
install myComp using myObjType $self.myComp args...
set myComp [myObjType $self.myComp args...]
- Note that whichever method is used, compName must still be declared
in the type definition using component, or must be referenced in at
least one delegate statement.
If this is a snit::widget or snit::widgetadaptor, and if
options have been delegated to component compName, then those
options will receive default values from the Tk option database. Note that
it doesn't matter whether the component to be installed is a widget or
not. See The Tk Option Database for more information.
install cannot be used to install type components; just assign the
type component's command name to the type component's variable
instead.
- installhull using widgetType args...
- installhull name
- The constructor of a snit::widgetadaptor must create a widget to be
the object's hull component; the widget is installed as the hull component
using this command. Note that the installed widget's name must be
$win. This command has two forms.
The first form specifies the widgetType and the args... (that
is, the hardcoded option list) to use in creating the hull. Given this
form, installhull creates the hull widget, and initializes any
options delegated to the hull from the Tk option database.
In the second form, the hull widget has already been created; note that its
name must be "$win". In this case, the Tk option database is
not queried for any options delegated to the hull. The longer form
is preferred; however, the shorter form allows the programmer to adapt a
widget created elsewhere, which is sometimes useful. For example, it can
be used to adapt a "page" widget created by a BWidgets
tabbed notebook or pages manager widget.
See The Tk Option Database for more information about
snit::widgetadaptors and the option database.
- variable name
- Normally, instance variables are defined in the type definition along with
the options, methods, and so forth; such instance variables are
automatically visible in all instance code (e.g., method bodies). However,
instance code can use the variable command to declare instance
variables that don't appear in the type definition, and also to bring
variables from other namespaces into scope in the usual way.
It's generally clearest to define all instance variables in the type
definition, and omit declaring them in methods and so forth.
Note that this is an instance-specific version of the standard Tcl
::variable command.
- typevariable name
- Normally, type variables are defined in the type definition, along with
the instance variables; such type variables are automatically visible in
all of the type's code. However, type methods, instance methods and so
forth can use typevariable to declare type variables that don't
appear in the type definition.
It's generally clearest to declare all type variables in the type
definition, and omit declaring them in methods, type methods, etc.
- varname name
- Deprecated. Use myvar instead.
Given an instance variable name, returns the fully qualified name. Use this
if you're passing the variable to some other object, e.g., as a
-textvariable to a Tk label widget.
- typevarname name
- Deprecated. Use mytypevar instead.
Given a type variable name, returns the fully qualified name. Use this if
you're passing the type variable to some other object, e.g., as a
-textvariable to a Tk label widget.
- codename name
- Deprecated. Use myproc instead. Given the name of a proc
(but not a type or instance method), returns the fully-qualified command
name, suitable for passing as a callback.
COMPONENTS AND DELEGATION¶
When an object includes other objects, as when a toolbar contains buttons or a
GUI object contains an object that references a database, the included object
is called a component. The standard way to handle component objects owned by a
Snit object is to declare them using
component, which creates a
component instance variable. In the following example, a
dog object has
a
tail object:
snit::type dog {
component mytail
constructor {args} {
set mytail [tail %AUTO% -partof $self]
$self configurelist $args
}
method wag {} {
$mytail wag
}
}
snit::type tail {
option -length 5
option -partof
method wag {} { return "Wag, wag, wag."}
}
Because the
tail object's name is stored in an instance variable, it's
easily accessible in any method.
The
install command provides an alternate way to create and install the
component:
snit::type dog {
component mytail
constructor {args} {
install mytail using tail %AUTO% -partof $self
$self configurelist $args
}
method wag {} {
$mytail wag
}
}
For
snit::types, the two methods are equivalent; for
snit::widgets
and
snit::widgetadaptors, the
install command properly
initializes the widget's options by querying
The Tk Option Database.
In the above examples, the
dog object's
wag method simply calls
the
tail component's
wag method. In OO jargon, this is called
delegation. Snit provides an easier way to do this:
snit::type dog {
delegate method wag to mytail
constructor {args} {
install mytail using tail %AUTO% -partof $self
$self configurelist $args
}
}
The
delegate statement in the type definition implicitly defines the
instance variable
mytail to hold the component's name (though it's good
form to use
component to declare it explicitly); it also defines the
dog object's
wag method, delegating it to the
mytail
component.
If desired, all otherwise unknown methods can be delegated to a specific
component:
snit::type dog {
delegate method * to mytail
constructor {args} {
set mytail [tail %AUTO% -partof $self]
$self configurelist $args
}
method bark { return "Bark, bark, bark!" }
}
In this case, a
dog object will handle its own
bark method; but
wag will be passed along to
mytail. Any other method, being
recognized by neither
dog nor
tail, will simply raise an error.
Option delegation is similar to method delegation, except for the interactions
with the Tk option database; this is described in
The Tk Option
Database.
TYPE COMPONENTS AND DELEGATION¶
The relationship between type components and instance components is identical to
that between type variables and instance variables, and that between type
methods and instance methods. Just as an instance component is an instance
variable that holds the name of a command, so a type component is a type
variable that holds the name of a command. In essence, a type component is a
component that's shared by every instance of the type.
Just as
delegate method can be used to delegate methods to instance
components, as described in
Components and Delegation, so
delegate
typemethod can be used to delegate type methods to type components.
Note also that as of Snit 0.95
delegate method can delegate methods to
both instance components and type components.
THE TK OPTION DATABASE¶
This section describes how Snit interacts with the Tk option database, and
assumes the reader has a working knowledge of the option database and its
uses. The book
Practical Programming in Tcl and Tk by Welch et al has a
good introduction to the option database, as does
Effective Tcl/Tk
Programming.
Snit is implemented so that most of the time it will simply do the right thing
with respect to the option database, provided that the widget developer does
the right thing by Snit. The body of this section goes into great deal about
what Snit requires. The following is a brief statement of the requirements,
for reference.
- •
- If the snit::widget's default widget class is not what is desired,
set it explicitly using widgetclass in the widget definition.
- •
- When defining or delegating options, specify the resource and class names
explicitly when if the defaults aren't what you want.
- •
- Use installhull using to install the hull for
snit::widgetadaptors.
- •
- Use install to install all other components.
The interaction of Tk widgets with the option database is a complex thing; the
interaction of Snit with the option database is even more so, and repays
attention to detail.
Setting the widget class: Every Tk widget has a widget class. For Tk
widgets, the widget class name is the just the widget type name with an
initial capital letter, e.g., the widget class for
button widgets is
"Button".
Similarly, the widget class of a
snit::widget defaults to the unqualified
type name with the first letter capitalized. For example, the widget class of
snit::widget ::mylibrary::scrolledText { ... }
is "ScrolledText". The widget class can also be set explicitly using
the
widgetclass statement within the
snit::widget definition.
Any widget can be used as the
hulltype provided that it supports the
-class option for changing its widget class name. See the discussion of
the
hulltype command, above. The user may pass
-class to the
widget at instantion.
The widget class of a
snit::widgetadaptor is just the widget class of its
hull widget; this cannot be changed unless the hull widget supports
-class, in which case it will usually make more sense to use
snit::widget rather than
snit::widgetadaptor.
Setting option resource names and classes: In Tk, every option has three
names: the option name, the resource name, and the class name. The option name
begins with a hyphen and is all lowercase; it's used when creating widgets,
and with the
configure and
cget commands.
The resource and class names are used to initialize option default values by
querying the Tk option database. The resource name is usually just the option
name minus the hyphen, but may contain uppercase letters at word boundaries;
the class name is usually just the resource name with an initial capital, but
not always. For example, here are the option, resource, and class names for
several
text widget options:
-background background Background
-borderwidth borderWidth BorderWidth
-insertborderwidth insertBorderWidth BorderWidth
-padx padX Pad
As is easily seen, sometimes the resource and class names can be inferred from
the option name, but not always.
Snit options also have a resource name and a class name. By default, these names
follow the rule given above: the resource name is the option name without the
hyphen, and the class name is the resource name with an initial capital. This
is true for both locally-defined options and explicitly delegated options:
snit::widget mywidget {
option -background
delegate option -borderwidth to hull
delegate option * to text
# ...
}
In this case, the widget class name is "Mywidget". The widget has the
following options:
-background, which is locally defined, and
-borderwidth, which is explicitly delegated; all other widgets are
delegated to a component called "text", which is probably a Tk
text widget. If so,
mywidget has all the same options as a
text widget. The option, resource, and class names are as follows:
-background background Background
-borderwidth borderwidth Borderwidth
-padx padX Pad
Note that the locally defined option,
-background, happens to have the
same three names as the standard Tk
-background option; and
-pad, which is delegated implicitly to the
text component, has
the same three names for
mywidget as it does for the
text
widget.
-borderwidth, on the other hand, has different resource and
class names than usual, because the internal word "width" isn't
capitalized. For consistency, it should be; this is done as follows:
snit::widget mywidget {
option -background
delegate option {-borderwidth borderWidth} to hull
delegate option * to text
# ...
}
The class name will default to "BorderWidth", as expected.
Suppose, however, that
mywidget also delegated
-padx and
-pady to the hull. In this case, both the resource name and the class
name must be specified explicitly:
snit::widget mywidget {
option -background
delegate option {-borderwidth borderWidth} to hull
delegate option {-padx padX Pad} to hull
delegate option {-pady padY Pad} to hull
delegate option * to text
# ...
}
Querying the option database: If you set your widgetclass and option
names as described above, Snit will query the option database when each
instance is created, and will generally do the right thing when it comes to
querying the option database. The remainder of this section goes into the gory
details.
Initializing locally defined options: When an instance of a snit::widget
is created, its locally defined options are initialized as follows: each
option's resource and class names are used to query the Tk option database. If
the result is non-empty, it is used as the option's default; otherwise, the
default hardcoded in the type definition is used. In either case, the default
can be overridden by the caller. For example,
option add *Mywidget.texture pebbled
snit::widget mywidget {
option -texture smooth
# ...
}
mywidget .mywidget -texture greasy
Here,
-texture would normally default to "smooth", but because
of the entry added to the option database it defaults to "pebbled".
However, the caller has explicitly overridden the default, and so the new
widget will be "greasy".
Initializing options delegated to the hull: A
snit::widget's hull
is a widget, and given that its class has been set it is expected to query the
option database for itself. The only exception concerns options that are
delegated to it with a different name. Consider the following code:
option add *Mywidget.borderWidth 5
option add *Mywidget.relief sunken
option add *Mywidget.hullbackground red
option add *Mywidget.background green
snit::widget mywidget {
delegate option -borderwidth to hull
delegate option -hullbackground to hull as -background
delegate option * to hull
# ...
}
mywidget .mywidget
set A [.mywidget cget -relief]
set B [.mywidget cget -hullbackground]
set C [.mywidget cget -background]
set D [.mywidget cget -borderwidth]
The question is, what are the values of variables A, B, C and D?
The value of A is "sunken". The hull is a Tk frame that has been given
the widget class "Mywidget"; it will automatically query the option
database and pick up this value. Since the
-relief option is implicitly
delegated to the hull, Snit takes no action.
The value of B is "red". The hull will automatically pick up the value
"green" for its
-background option, just as it picked up the
-relief value. However, Snit knows that
-hullbackground is
mapped to the hull's
-background option; hence, it queries the option
database for
-hullbackground and gets "red" and updates the
hull accordingly.
The value of C is also "red", because
-background is implicitly
delegated to the hull; thus, retrieving it is the same as retrieving
-hullbackground. Note that this case is unusual; in practice,
-background would probably be explicitly delegated to some other
component.
The value of D is "5", but not for the reason you think. Note that as
it is defined above, the resource name for
-borderwidth defaults to
"borderwidth", whereas the option database entry is
"borderWidth". As with
-relief, the hull picks up its own
-borderwidth option before Snit does anything. Because the option is
delegated under its own name, Snit assumes that the correct thing has
happened, and doesn't worry about it any further.
For
snit::widgetadaptors, the case is somewhat altered. Widget adaptors
retain the widget class of their hull, and the hull is not created
automatically by Snit. Instead, the
snit::widgetadaptor must call
installhull in its constructor. The normal way to do this is as
follows:
snit::widgetadaptor mywidget {
# ...
constructor {args} {
# ...
installhull using text -foreground white
#
}
#...
}
In this case, the
installhull command will create the hull using a
command like this:
set hull [text $win -foreground white]
The hull is a
text widget, so its widget class is "Text". Just
as with
snit::widget hulls, Snit assumes that it will pick up all of
its normal option values automatically; options delegated from a different
name are initialized from the option database in the same way.
Initializing options delegated to other components: Non-hull components
are matched against the option database in two ways. First, a component widget
remains a widget still, and therefore is initialized from the option database
in the usual way. Second, the option database is queried for all options
delegated to the component, and the component is initialized
accordingly--provided that the
install command is used to create it.
Before option database support was added to Snit, the usual way to create a
component was to simply create it in the constructor and assign its command
name to the component variable:
snit::widget mywidget {
delegate option -background to myComp
constructor {args} {
set myComp [text $win.text -foreground black]
}
}
The drawback of this method is that Snit has no opportunity to initialize the
component properly. Hence, the following approach is now used:
snit::widget mywidget {
delegate option -background to myComp
constructor {args} {
install myComp using text $win.text -foreground black
}
}
The
install command does the following:
- •
- Builds a list of the options explicitly included in the install
command -- in this case, -foreground.
- •
- Queries the option database for all options delegated explicitly to the
named component.
- •
- Creates the component using the specified command, after inserting into it
a list of options and values read from the option database. Thus, the
explicitly included options ( -foreground) will override anything
read from the option database.
- •
- If the widget definition implicitly delegated options to the component
using delegate option *, then Snit calls the newly created
component's configure method to receive a list of all of the
component's options. From this Snit builds a list of options implicitly
delegated to the component that were not explicitly included in the
install command. For all such options, Snit queries the option
database and configures the component accordingly.
Non-widget components: The option database is never queried for
snit::types, since it can only be queried given a Tk widget name.
However,
snit::widgets can have non-widget components. And if options
are delegated to those components, and if the
install command is used
to install those components, then they will be initialized from the option
database just as widget components are.
The
snit::macro command enables a certain amount of meta-programming with
Snit classes. For example, suppose you like to define properties: instance
variables that have set/get methods. Your code might look like this:
snit::type dog {
variable mood happy
method getmood {} {
return $mood
}
method setmood {newmood} {
set mood $newmood
}
}
That's nine lines of text per property. Or, you could define the following
snit::macro:
snit::macro property {name initValue} {
variable $name $initValue
method get$name {} "return $name"
method set$name {value} "set $name \$value"
}
Note that a
snit::macro is just a normal Tcl proc defined in the slave
interpreter used to compile type and widget definitions; as a result, it has
access to all the commands used to define types and widgets.
Given this new macro, you can define a property in one line of code:
snit::type dog {
property mood happy
}
Within a macro, the commands
variable and
proc refer to the Snit
type-definition commands, not the standard Tcl commands. To get the standard
Tcl commands, use
_variable and
_proc.
Because a single slave interpreter is used for compiling all Snit types and
widgets in the application, there's the possibility of macro name collisions.
If you're writing a reuseable package using Snit, and you use some
snit::macros, define them in your package namespace:
snit::macro mypkg::property {name initValue} { ... }
snit::type dog {
mypkg::property mood happy
}
This leaves the global namespace open for application authors.
VALIDATION TYPES¶
A validation type is an object that can be used to validate Tcl values of a
particular kind. For example,
snit::integer is used to validate that a
Tcl value is an integer.
Every validation type has a
validate method which is used to do the
validation. This method must take a single argument, the value to be
validated; further, it must do nothing if the value is valid, but throw an
error if the value is invalid:
snit::integer validate 5 ;# Does nothing
snit::integer validate 5.0 ;# Throws an error (not an integer!)
The
validate method will always return the validated value on success,
and throw the
-errorcode INVALID on error.
Snit defines a family of validation types, all of which are implemented as
snit::type's. They can be used as is; in addition, their instances
serve as parameterized subtypes. For example, a probability is a number
between 0.0 and 1.0 inclusive:
snit::double probability -min 0.0 -max 1.0
The example above creates an instance of
snit::double--a validation
subtype--called
probability, which can be used to validate probability
values:
probability validate 0.5 ;# Does nothing
probability validate 7.9 ;# Throws an error
Validation subtypes can be defined explicitly, as in the above example; when a
locally-defined option's
-type is specified, they may also be created
on the fly:
snit::enum ::dog::breed -values {mutt retriever sheepdog}
snit::type dog {
# Define subtypes on the fly...
option -breed -type {
snit::enum -values {mutt retriever sheepdog}
}
# Or use predefined subtypes...
option -breed -type ::dog::breed
}
Any object that has a
validate method with the semantics described above
can be used as a validation type; see
Defining Validation Types for
information on how to define new ones.
Snit defines the following validation types:
- snit::boolean validate ?value?
- snit::boolean name
- Validates Tcl boolean values: 1, 0, on, off, yes,
no, true, false. It's possible to define
subtypes--that is, instances--of snit::boolean, but as it has no
options there's no reason to do so.
- snit::double validate ?value?
- snit::double name ?option value...?
- Validates floating-point values. Subtypes may be created with the
following options:
- -min min
- Specifies a floating-point minimum bound; a value is invalid if it is
strictly less than min.
- -max max
- Specifies a floating-point maximum bound; a value is invalid if it is
strictly greater than max.
- snit::enum validate ?value?
- snit::enum name ?option value...?
- Validates that a value comes from an enumerated list. The base type is of
little use by itself, as only subtypes actually have an enumerated list to
validate against. Subtypes may be created with the following options:
- -values list
- Specifies a list of valid values. A value is valid if and only if it's
included in the list.
- snit::fpixels validate ?value?
- snit::fpixels name ?option value...?
- Tk programs only. Validates screen distances, in any of the forms
accepted by winfo fpixels. Subtypes may be created with the
following options:
- -min min
- Specifies a minimum bound; a value is invalid if it is strictly less than
min. The bound may be expressed in any of the forms accepted by
winfo fpixels.
- -max max
- Specifies a maximum bound; a value is invalid if it is strictly greater
than max. The bound may be expressed in any of the forms accepted
by winfo fpixels.
- snit::integer validate ?value?
- snit::integer name ?option value...?
- Validates integer values. Subtypes may be created with the following
options:
- -min min
- Specifies an integer minimum bound; a value is invalid if it is strictly
less than min.
- -max max
- Specifies an integer maximum bound; a value is invalid if it is strictly
greater than max.
- snit::listtype validate ?value?
- snit::listtype name ?option value...?
- Validates Tcl lists. Subtypes may be created with the following
options:
- -minlen min
- Specifies a minimum list length; the value is invalid if it has fewer than
min elements. Defaults to 0.
- -maxlen max
- Specifies a maximum list length; the value is invalid if it more than
max elements.
- -type type
- Specifies the type of the list elements; type must be the name of a
validation type or subtype. In the following example, the value of
-numbers must be a list of integers.
option -numbers -type {snit::listtype -type snit::integer}
- Note that this option doesn't support defining new validation subtypes on
the fly; that is, the following code will not work (yet, anyway):
option -numbers -type {
snit::listtype -type {snit::integer -min 5}
}
- Instead, define the subtype explicitly:
snit::integer gt4 -min 5
snit::type mytype {
option -numbers -type {snit::listtype -type gt4}
}
- snit::pixels validate ?value?
- snit::pixels name ?option value...?
- Tk programs only. Validates screen distances, in any of the forms
accepted by winfo pixels. Subtypes may be created with the
following options:
- -min min
- Specifies a minimum bound; a value is invalid if it is strictly less than
min. The bound may be expressed in any of the forms accepted by
winfo pixels.
- -max max
- Specifies a maximum bound; a value is invalid if it is strictly greater
than max. The bound may be expressed in any of the forms accepted
by winfo pixels.
- snit::stringtype validate ?value?
- snit::stringtype name ?option value...?
- Validates Tcl strings. The base type is of little use by itself, since
very Tcl value is also a valid string. Subtypes may be created with the
following options:
- -minlen min
- Specifies a minimum string length; the value is invalid if it has fewer
than min characters. Defaults to 0.
- -maxlen max
- Specifies a maximum string length; the value is invalid if it has more
than max characters.
- -glob pattern
- Specifies a string match pattern; the value is invalid if it
doesn't match the pattern.
- -regexp regexp
- Specifies a regular expression; the value is invalid if it doesn't match
the regular expression.
- -nocase flag
- By default, both -glob and -regexp matches are
case-sensitive. If -nocase is set to true, then both -glob
and -regexp matches are case-insensitive.
- snit::window validate ?value?
- snit::window name
- Tk programs only. Validates Tk window names. The value must cause
winfo exists to return true; otherwise, the value is invalid. It's
possible to define subtypes--that is, instances--of snit::window,
but as it has no options at present there's no reason to do so.
DEFINING VALIDATION TYPES¶
There are three ways to define a new validation type: as a subtype of one of
Snit's validation types, as a validation type command, and as a full-fledged
validation type similar to those provided by Snit. Defining subtypes of Snit's
validation types is described above, under
Validation Types.
The next simplest way to create a new validation type is as a validation type
command. A validation type is simply an object that has a
validate
method; the
validate method must take one argument, a value, return the
value if it is valid, and throw an error with
-errorcode INVALID if the
value is invalid. This can be done with a simple
proc. For example, the
snit::boolean validate type could have been implemented like this:
proc ::snit::boolean {"validate" value} {
if {![string is boolean -strict $value]} {
return -code error -errorcode INVALID "invalid boolean \"$value\", should be one of: 1, 0, ..."
}
return $value
}
A validation type defined in this way cannot be subtyped, of course; but for
many applications this will be sufficient.
Finally, one can define a full-fledged, subtype-able validation type as a
snit::type. Here's a skeleton to get you started:
snit::type myinteger {
# First, define any options you'd like to use to define
# subtypes. Give them defaults such that they won't take
# effect if they aren't used, and marked them "read-only".
# After all, you shouldn't be changing their values after
# a subtype is defined.
#
# For example:
option -min -default "" -readonly 1
option -max -default "" -readonly 1
# Next, define a "validate" type method which should do the
# validation in the basic case. This will allow the
# type command to be used as a validation type.
typemethod validate {value} {
if {![string is integer -strict $value]} {
return -code error -errorcode INVALID "invalid value \"$value\", expected integer"
}
return $value
}
# Next, the constructor should validate the subtype options,
# if any. Since they are all readonly, we don't need to worry
# about validating the options on change.
constructor {args} {
# FIRST, get the options
$self configurelist $args
# NEXT, validate them.
# I'll leave this to your imagination.
}
# Next, define a "validate" instance method; its job is to
# validate values for subtypes.
method validate {value} {
# First, call the type method to do the basic validation.
$type validate $value
# Now we know it's a valid integer.
if {("" != $options(-min) && $value < $options(-min)) ||
("" != $options(-max) && $value > $options(-max))} {
# It's out of range; format a detailed message about
# the error, and throw it.
set msg "...."
return -code error -errorcode INVALID $msg
}
# Otherwise, if it's valid just return it.
return $valid
}
}
And now you have a type that can be subtyped.
The file "validate.tcl" in the Snit distribution defines all of Snit's
validation types; you can find the complete implementation for
snit::integer and the other types there, to use as examples for your
own types.
CAVEATS¶
If you have problems, find bugs, or new ideas you are hereby cordially invited
to submit a report of your problem, bug, or idea as explained in the section
Bugs, Ideas, Feedback below.
Additionally, you might wish to join the Snit mailing list; see
http://www.wjduquette.com/snit for details.
One particular area to watch is using
snit::widgetadaptor to adapt
megawidgets created by other megawidget packages; correct widget destruction
depends on the order of the <Destroy> bindings. The wisest course is
simply not to do this.
KNOWN BUGS¶
- •
- Error stack traces returned by Snit 1.x are extremely ugly and typically
contain far too much information about Snit internals. The error messages
are much improved in Snit 2.2.
- •
- Also see the Project Trackers as explained in the section Bugs, Ideas,
Feedback below.
HISTORY¶
During the course of developing Notebook (See
http://www.wjduquette.com/notebook), my Tcl-based personal notebook
application, I found I was writing it as a collection of objects. I wasn't
using any particular object-oriented framework; I was just writing objects in
pure Tcl following the guidelines in my Guide to Object Commands (see
http://www.wjduquette.com/tcl/objects.html), along with a few other
tricks I'd picked up since. And though it was working well, it quickly became
tiresome because of the amount of boilerplate code associated with each new
object type.
So that was one thing--tedium is a powerful motivator. But the other thing I
noticed is that I wasn't using inheritance at all, and I wasn't missing it.
Instead, I was using delegation: objects that created other objects and
delegated methods to them.
And I said to myself, "This is getting tedious...there has got to be a
better way." And one afternoon, on a whim, I started working on Snit, an
object system that works the way Tcl works. Snit doesn't support inheritance,
but it's great at delegation, and it makes creating megawidgets easy.
If you have any comments or suggestions (or bug reports!) don't hesitate to send
me e-mail at
will@wjduquette.com. In addition, there's a Snit mailing
list; you can find out more about it at the Snit home page (see
http://www.wjduquette.com/snit).
CREDITS¶
Snit has been designed and implemented from the very beginning by William H.
Duquette. However, much credit belongs to the following people for using Snit
and providing me with valuable feedback: Rolf Ade, Colin McCormack, Jose
Nazario, Jeff Godfrey, Maurice Diamanti, Egon Pasztor, David S. Cargo, Tom
Krehbiel, Michael Cleverly, Andreas Kupries, Marty Backe, Andy Goth, Jeff
Hobbs, Brian Griffin, Donal Fellows, Miguel Sofer, Kenneth Green, and Anton
Kovalenko. If I've forgotten anyone, my apologies; let me know and I'll add
your name to the list.
BUGS, IDEAS, FEEDBACK¶
This document, and the package it describes, will undoubtedly contain bugs and
other problems. Please report such in the category
snit of the
Tcllib Trackers [
http://core.tcl.tk/tcllib/reportlist]. Please also
report any ideas for enhancements you may have for either package and/or
documentation.
KEYWORDS¶
BWidget, C++, Incr Tcl, Snit, adaptors, class, mega widget, object, object
oriented, type, widget, widget adaptors
CATEGORY¶
Programming tools
COPYRIGHT¶
Copyright (c) 2003-2009, by William H. Duquette