NAME¶
perl5i::Meta - The perl5i meta object
SYNOPSIS¶
use perl5i;
my $id = $object->mo->id;
my $class = $object->mc->class;
my $tainted = $object->mo->is_tainted;
...and so on...
DESCRIPTION¶
Each object has a meta object which can be used to describe and sometimes alter
the object. This is for things which are common to *all* objects. For example,
"$obj->mc->class" to get the object's class. "@ISA =
$obj->mc->ISA" to get an object's parents. And so on.
Why not just stick these methods in UNIVERSAL? They'd clash with user-space
methods. For example, if an existing class has its own "id()" method
it would likely clash with what our "id()" method does. You want to
guarantee that every object responds to these meta methods the same way so
there's no second-guessing.
Each object has a meta object for their instance, accessible with
"$obj->mo" and also a meta object for their class, accessible
with "$obj->mc". The meta instance can do most everything the
meta class can, mc is provided mostly for disambiguation.
The problem is this:
my $thing = "Foo";
say $thing->mo->class;
In perl5i, everything is an object. Do you want the class of $thing or do you
want to treat $thing as a class name? Its ambiguous. So to disambiguate, use
"$thing->mc" when you mean $thing to be a class name and
"$thing->mo" when you mean it to be an object.
For example, when writing a method which could be a class or could be an object
be sure to use "$proto->mc->class" to get the class name.
sub my_method {
my $proto = shift; # could be an object, could be a class name
my $class = $proto->mc->class;
....
}
METHODS¶
id
my $id = $object->mo->id;
Returns an identifer for $object.
The identifier is guaranteed to be:
* unique to the object for the life of the process
* a true value
* independent of changes to the object's contents
class
my $class = $object->mo->class;
my $class = $class->mc->class;
Returns the class of the $object or $class.
ISA
my @ISA = $object->mo->ISA;
my @ISA = $class->mc->ISA;
Returns the immediate parents of the $class or $object.
Essentially equivalent to:
no strict 'refs';
my @ISA = @{$class.'::ISA'};
linear_isa
my @isa = $class->mc->linear_isa();
my @isa = $object->mo->linear_isa();
Returns the entire inheritance tree of the $class or $object as a list in the
order it will be searched for method inheritance.
This list includes the $class itself and includes UNIVERSAL. For example:
package Child;
use parent qw(Parent);
# Child, Parent, UNIVERSAL
my @isa = Child->mo->linear_isa();
methods
my @methods = $class->mc->methods;
my $methods = $class->mc->methods;
my @methods = $object->mo->methods;
my $methods = $object->mo->methods;
my $methods = $object->mo->methods({
with_UNIVERSAL => 0,
just_mine => 1,
});
Returns the methods available to a $class or $object.
By default it returns all the methods available
except those inherited
from UNIVERSAL because you usually don't want to know that.
"with_UNIVERSAL", if true, makes it include methods inherited from
UNIVERSAL. It defaults to false.
"just_mine", if true, returns only methods defined in the $class. It
defaults to false.
symbol_table
my $table = $class->mc->symbol_table;
my $table = $obj->mo->symbol_table;
Returns the symbol table for the given $class or class of the $object.
If you don't know what a symbol table is... good. If you really want to know,
see "Typeglobs and FileHandles" in perldata.
super
my @return = $class->mc->super(@args);
my @return = $object->mo->super(@args);
Call the parent of $class/$object's implementation of the current method.
Equivalent to "$object->SUPER::method(@args)" but based on the
class of the $object rather than the class in which the current method was
declared.
is_tainted
my $is_tainted = $object->mo->is_tainted;
Returns true if the $object is tainted.
Only scalars can be tainted, so objects generally return false.
String and numerically overloaded objects will check against their overloaded
versions.
taint
$object->mo->taint;
Taints the $object.
Normally only scalars can be tainted, this will throw an exception on anything
else.
Tainted, string overloaded objects will cause this to be a no-op.
An object can override this method if they have a means of tainting themselves.
Generally this is applicable to string or numeric overloaded objects who can
taint their overloaded value.
untaint
$object->mo->untaint;
Untaints the $object.
Normally objects cannot be tainted, so it is a no op on anything but a scalar.
Tainted, string overloaded objects will throw an exception.
An object can override this method if they have a means of untainting
themselves. Generally this is applicable to string or numeric overloaded
objects who can untaint their overloaded value.
reftype
my $reftype = $object->mo->reftype;
Returns the underlying reference type of the $object.
checksum
my $checksum = $object->mo->checksum;
my $md5 = $object->mo->checksum( algorithm => 'md5' );
my $base64 = $object->mo->checksum( format => 'base64' );
Get a digest of the object's contents, taking its class into account.
Two different objects can have the same checksum if their contents are
identical. Likewise, a single object can have different checksums throughout
its life cycle if it's mutable. This means its checksum will change if its
internal state changes.
For example,
$obj->mo->checksum( format => 'base64', algorithm => 'md5' );
options
- algorithm
- The checksum algorithm. Can be "sha1" and "md5".
Defaults to sha1.
- format
- The character set of the checksum, can be "hex",
"base64", or "binary".
Defaults to hex.
is_equal
$object->mo->is_equal($other_object)
Assess whether something is equal to something else, recurring over deep data
structures and treating overloaded objects as numbers or strings when
appropriate.
Examples:
my $prices = { chair => 50, table => 300 };
my $other = { chair => 50, table => [250, 255] };
say "They are equal" if $prices->mo->is_equal($other);
my $uri = URI->new("http://www.perl.org");
$uri->mo->is_equal("http://www.perl.org") # True
perl
Same as as_perl. For backwards compatibility.
as_perl
my $dump = $object->mo->as_perl;
Dumps the contents of the $object as Perl in a string, like Data::Dumper.
as_json
my $json = $object->mo->as_json;
Return the contents of the $object as JSON.
as_yaml
my $json = $object->mo->as_yaml;
Return the contents of the $object as YAML.
dump
my $dump = $object->mo->dump( format => $format );
Dumps the contents of the $object as a string in whatever format you like.
Possible formats are yaml, json and perl.
$format defaults to "perl" which is equivalent to
"$object->mo->perl".
This is simply the long form of "as_perl", "as_json" and
"as_yaml".