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10 non-PAUSE user(s).

Michael G Schwern

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 a meta object?

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.

Meta Instance vs Meta Class

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.




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