NAME¶
gencls - class interface compiler for Prima core modules
SYNOPSIS¶
gencls --h --inc --tml -O -I<name> --depend --sayparent filename.cls
DESCRIPTION¶
Creates headers with C macros and structures for Prima core module object
definitions.
ARGUMENTS¶
gencls accepts the following arguments:
- --h
- Generates .h file ( with declarations to be included in one or more files
)
- --inc
- Generates .inc file ( with declarations to be included in only file )
- -O
- Turns optimizing algorithm for .inc files on. Algorithm is based on an
assumption, that some functions are declared identically, therefore the
code piece that handles the parameter and result conversion can be shared.
With "-O" flag on, a thunk body is replaced to a call to a
function, which name is made up from all method parameters plus result.
Actual function is not written in .inc file, but in .tml file. All
duplicate declarations from a set of .tml files can be removed and the
reminder written to one file by tmlink utility.
- --tml
- Generates .tml file. Turns "-O" automatically on.
- -Idirname
- Adds a directory to a search path, where the utility searches for .cls
files. Can be specified several times.
- --depend
- Prints out dependencies for a given file.
- --sayparent
- Prints out the immediate parent of a class inside given file.
SYNTAX¶
In short, the syntax of a .cls file can be described by the following scheme:
[ zero or more type declarations ]
[ zero or one class declaration ]
Gencls produces .h, .inc or .tml files, with a base name of the .cls file, if no
object or package name given, or with a name of the object or the package
otherwise.
Basic scalar data types¶
Gencls has several built-in scalar data types, that it knows how to deal with.
To 'deal' means that it can generate a code that transfers data of these types
between C and perl, using XS ( see perlguts ) library interface.
The types are:
int
Bool
Handle
double
SV*
HV*
char *
string ( C declaration is char[256] )
There are also some derived built-in types, which are
long
short
char
Color
U8
that are mapped to int. The data undergo no conversion to int in transfer
process, but it is stored instead to perl scalar using
newSViv()
function, which, in turn, may lose bits or a sign.
Derived data types¶
The syntax for a new data types definition is as follows:
<scope> <prefix> <id> <definition>
A scope can be one of two pragmas, "global" or "local". They
hint the usage of a new data type, whether the type will be used only for one
or more objects. Usage of "local" is somewhat resembles C pragma
static. Currently the only difference is that a function using a complex local
type in the parameter list or as the result is not a subject for
"-O" optimization.
Scalar types¶
New scalar types may only be aliased to the existing ones, primarily for C
coding convenience. A scalar type can be defined in two ways:
- Direct aliasing
- Syntax:
<scope> $id => <basic_scalar_type>;
Example:
global $Handle => int;
The new type id will not be visible in C files, but the type will be
substituted over all .cls files that include this definition.
- C macro
- Syntax:
<scope> id1 id2
Example:
global API_HANDLE UV
Such code creates a C macro definition in .h header file in form
#define id1 id2
C macros with parameters are not allowed. id1 and id2 are not required to be
present in .cls name space, and no substitution during .cls file
processing is made. This pragma usage is very limited.
Complex types¶
Complex data types can be arrays, structs and hashes. They can be a combination
or a vector of scalar ( but not complex) data types.
Gencls allows several combinations of complex data types that C language does
not recognize. These will be described below.
Complex data types do not get imported into perl code. A perl programmer must
conform to the data type used when passing parameters to a function.
- Arrays
- Syntax:
<scope> @id <basic_scalar_type>[dimension];
Example:
global @FillPattern U8[8];
Example of functions using arrays:
Array * func( Array a1, Array * a2);
Perl code:
@ret = func( @array1, @array2);
Note that array references are not used, and the number of items in all
array parameters must be exactly as the dimensions of the arrays.
Note: the following declaration will not compile with C compiler, as C
cannot return arrays. However it is not treated as an error by gencls:
Array func();
- Structs
- Syntax:
<scope> @id {
<basic_scalar_type> <id>;
...
<basic_scalar_type> <id>;
};
Example:
global @Struc {
int number;
string id;
}
Example of functions using structs:
Struc * func1( Struc a1, Struc * a2);
Struc func2( Struc a1, Struc * a2);
Perl code:
@ret = func1( @struc1, @struc2);
@ret = func2( @struc1, @struc2);
Note that array references are not used, and both number and order of items
in all array parameters must be set exactly as dimensions and order of the
structs. Struct field names are not used in perl code as well.
- Hashes
- Syntax:
<scope> %id {
<basic_scalar_type> <id>;
...
<basic_scalar_type> <id>;
};
Example:
global %Hash {
int number;
string id;
}
Example of functions using hashes:
Hash * func1( Hash a1, Hash * a2);
Hash func2( Hash a1, Hash * a2);
Perl code:
%ret = %{func1( \%hash1, \%hash2)};
%ret = %{func2( \%hash1, \%hash2)};
Note that only hash references are used and returned. When a hash is passed
from perl code it might have some or all fields unset. The C structure is
filled and passed to a C function, and the fields that were unset are
assigned to a corresponding C_TYPE_UNDEF value, where TYPE is one of
NUMERIC, STRING and POINTER literals.
Back conversion does not count on these values and always returns all hash
keys with a corresponding pair.
Namespace section¶
Syntax:
<namespace> <ID> {
<declaration>
...
<declaration>
}
A .cls file can have zero or one namespace sections, filled with function
descriptions. Functions described here will be exported to the given ID during
initialization code. A namespace can be either "object" or
"package".
The package namespace syntax allows only declaration of functions inside a
"package" block.
package <Package ID> {
<function description>
...
}
The object namespace syntax includes variables and properties as well as
functions ( called methods in the object syntax ). The general object
namespace syntax is
object <Class ID> [(Parent class ID)] {
<variables>
<methods>
<properties>
}
Within an object namespace the inheritance syntax can be used:
object <Class ID> ( <Parent class ID>) { ... }
or a bare root object description ( with no ancestor )
object <Class ID> { ... }
for the object class declaration.
Functions¶
Syntax:
[<prefix>] <type> <function_name> (<parameter list>) [ => <alias>];
Examples:
int package_func1( int a, int b = 1) => c_func_2;
Point package_func2( Struc * x, ...);
method void object_func3( HV * profile);
A prefix is used with object functions ( methods ) only. More on the prefix in
Methods section.
A function can return nothing ( void ), a scalar ( int, string, etc ) or a
complex ( array, hash ) type. It can as well accept scalar and complex
parameters, with type conversion that corresponds to the rules described above
in "Basic scalar data types" section.
If a function has parameters and/or result of a type that cannot be converted
automatically between C and perl, it gets declared but not exposed to perl
namespace. The corresponding warning is issued. It is not possible using
gencls syntax to declare a function with custom parameters or result data. For
such a purpose the explicit C declaration of code along with "newXS"
call must be made.
Example: ellipsis (...) cannot be converted by gencls, however it is a legal C
construction.
Point package_func2( Struc * x, ...);
The function syntax has several convenience additions:
- Default parameter values
- Example:
void func( int a = 15);
A function declared in such way can be called both with 0 or 1 parameters.
If it is called with 0 parameters, an integer value of 15 will be
automatically used. The syntax allows default parameters for types int,
pointer and string and their scalar aliases.
Default parameters can be as many as possible, but they have to be in the
end of the function parameter list. Declaration "func( int a = 1, int
b)" is incorrect.
- Aliasing
- In the generated C code, a C function has to be called after the
parameters have been parsed. Gencls expects a conformant function to be
present in C code, with fixed name and parameter list. However, if the
task of such function is a wrapper to an identical function published
under another name, aliasing can be preformed to save both code and speed.
Example:
package Package {
void func( int x) => internal;
}
A function declared in that way will not call Package_func() C
function, but internal() function instead. The only request is that
internal() function must have identical parameter and result
declaration to a func().
- Inline hash
- A handy way to call a function with a hash as a parameter from perl was
devised. If a function is declared with the last parameter or type
"HV*", then parameter translation from perl to C is performed as
if all the parameters passed were a hash. This hash is passed to a C
function and it's content returned then back to perl as a hash again. The
hash content can be modified inside the C function.
This declaration is used heavily in constructors, which perl code is typical
sub init
{
my %ret = shift-> SUPER::init( @_);
...
return %ret;
}
and C code is usually
void Obj_init ( HV * profile) {
inherited init( profile);
... [ modify profile content ] ...
}
Methods¶
Methods are functions called in a context of an object. Virtually all methods
need to have an access to an object they are dealing with. Prima objects are
visible in C as Handle data type. Such Handle is actually a pointer to an
object instance, which in turn contains a pointer to the object virtual
methods table ( VMT ). To facilitate an OO-like syntax, this Handle parameter
is almost never mentioned in all methods of an object description in a cls
file, although being implicit counted, so every cls method declaration
method void a( int x)
for an object class Object is reflected in C as
void Object_a( Handle self, int x)
function declaration. Contrary to package functions, that gencls is unable to
publish if it is unable to deal with the unsupported on unconvertible
parameters, there is a way to issue such a declaration with a method. The
primary use for that is the method name gets reserved in the object's VMT.
Methods are accessible in C code by the direct name dereferencing of a
"Handle self" as a corresponding structure:
((( PSampleObject) self)-> self)-> sample_method( self, ...);
A method can have one of six prefixes that govern C code generation:
- method
- This is the first and the most basic method type. It's prefix name,
"method" is therefore was chosen as the most descriptive name.
Methods are expected to be coded in C, the object handle is implicit and
is not included into a .cls description.
method void a()
results in
void Object_a( Handle self)
C declaration. A published method automatically converts its parameters and
a result between C and perl.
- public
- When the methods that have parameters and/or result that cannot be
automatically converted between C and perl need to be declared, or the
function declaration does not fit into C syntax, a "public"
prefix is used. The methods declared with "public" is expected
to communicate with perl by means of XS ( see perlxs ) interface. It is
also expected that a "public" method creates both REDEFINED and
FROMPERL functions ( see Prima::internals for details). Examples are many
throughout Prima source, and will not be shown here. "public"
methods usually have void result and no parameters, but that does not
matter much, since gencls produces no conversion for such methods.
- import
- For the methods that are unreasonable to code in C but in perl instead,
gencls can be told to produce the corresponding wrappers using
"import" prefix. This kind of a method can be seen as
"method" inside-out. "import" function does not need a
C counterpart, except the auto-generated code.
- static
- If a method has to be able to work both with and without an object
instance, it needs to be prepended with "static" prefix.
"static" methods are all alike "method" ones, except
that "Handle self" first parameter is not implicitly declared.
If a "static" method is called without an object ( but with a
class ), like
Class::Object-> static_method();
its first parameter is not a object but a "Class::Object" string.
If a method never deals with an object, it is enough to use its
declaration as
static a( char * className = "");
but is if does, a
static a( SV * class_or_object = nil);
declaration is needed. In latter case C code itself has to determine what
exactly has been passed, if ever. Note the default parameter here: a
"static" method is usually legible to call as
Class::Object::static_method();
where no parameters are passed to it. Without the default parameter such a
call generates an 'insufficient parameters passed' runtime error.
- weird
- We couldn't find a better name for it. "weird" prefix denotes a
method that combined properties both from "static" and
"public". In other words, gencls generates no conversion code
and expects no "Handle self" as a first parameter for such a
method. As an example Prima::Image::load can be depicted, which can be
called using a wide spectrum of calling semantics ( see Prima::image-load
for details).
- c_only
- As its name states, "c_only" is a method that is present on a
VMT but is not accessible from perl. It can be overloaded from C only.
Moreover, it is allowed to register a perl function with a name of a
"c_only" method, and still these entities will be wholly
independent from each other - the overloading will not take place.
NB: methods that have result and/or parameters data types that can not be
converted automatically, change their prefix to "c_only".
Probably this is the wrong behavior, and such condition have to signal an
error.
Properties¶
Prima toolkit introduces an entity named property, that is expected to replace
method pairs whose function is to acquire and assign some internal object
variable, for example, an object name, color etc. Instead of having pair of
methods like Object::set_color and Object::get_color, a property Object::color
is devised. A property is a method with the special considerations, in
particular, when it is called without parameters, a 'get' mode is implied. In
contrary, if it is called with one parameter, a 'set' mode is triggered. Note
that on both 'set' and 'get' invocations "Handle self" first
implicit parameter is always present.
Properties can operate with different, but fixed amount of parameters, and
perform a 'set' and 'get' functions only for one. By default the only
parameter is the implicit "Handle self":
property char * name
has C counterpart
char * Object_name( Handle self, Bool set, char * name)
Depending on a mode, "Bool set" is either "true" or
"false". In 'set' mode a C code result is discarded, in 'get' mode
the parameter value is undefined.
The syntax for multi-parameter property is
property long pixel( int x, int y);
and C code
long Object_pixel( Handle self, Bool set, int x, int y, long pixel)
Note that in the multi-parameter case the parameters declared after property
name are always initialized, in both 'set' and 'get' modes.
Instance variables¶
Every object is characterized by its unique internal state. Gencls syntax allows
a variable declaration, for variables that are allocated for every object
instance. Although data type validation is not performed for variables, and
their declarations just get copied 'as is', complex C declarations involving
array, struct and function pointers are not recognized. As a workaround,
pointers to typedef'd entities are used. Example:
object SampleObject {
int x;
List list;
struct { int x } s; # illegal declaration
}
Variables are accessible in C code by direct name dereferencing of a
"Handle self" as a corresponding structure:
(( PSampleObject) self)-> x;
AUTHORS¶
Dmitry Karasik, <dmitry@karasik.eu.org>. Anton Berezin,
<tobez@tobez.org>.
SEE ALSO¶
Prima::internals, tmlink
COPYRIGHT¶
This program is distributed under the BSD License.