Object::InsideOut::MetUseraContributed Perl DocuObject::InsideOut::Metadata(3)NAMEObject::InsideOut::Metadata - Introspection for Object::InsideOut
classes
VERSION
This document describes Object::InsideOut::Metadata version 3.81
SYNOPSIS
package My::Class; {
use Object::InsideOut;
use Object::InsideOut::Metadata;
my @data :Field :Arg('data') :Get('data') :Set('put_data');
my @misc :Field;
my %init_args :InitArgs = (
'INFO' => '',
);
sub _init :Init
{
my ($self, $args) = @_;
if (exists($args->{'INFO'})) {
$misc[$$self] = 'INFO: ' . $args->{'INFO'};
}
}
sub misc :lvalue :Method
{
my $self = shift;
$misc[$$self];
}
add_meta(__PACKAGE__, 'misc', { 'lvalue' => 1 });
}
package main;
# Obtain a metadata object for a class
my $meta = My::Class->meta();
# ... or obtain a metadata object for an object
my $obj = My::Class->new();
my $meta = $obj->meta();
# Obtain the class hierarchy from the metadata object
my @classes = $meta->get_classes();
# Obtain infomation on the parameters for a class's construction
my %args = $meta->get_args();
# Obtain information on a class's methods
my %methods = $meta->get_methods();
DESCRIPTION
Object::InsideOut provides an introspection API that allows you to
obtain metadata on a class's hierarchy, constructor parameters, and
methods. This is done through the use of metadata objects that are
generated by this class.
In addition, developers can specify metadata data for methods they
write for their classes.
METADATA OBJECT
To obtain metadata on an Object::InsideOut class or object, you must
first generate a metadata object for that class or object. Using that
metadata object, one can then obtain information on the class
hierarchy, constructor parameters, and methods.
my $meta = My::Class->meta();
my $meta = $obj->meta();
The "->meta()" method, which is exported by Object::InsideOut to
each class, returns an Object::InsideOut::Metadata object which can
then be queried for information about the invoking class or
invoking object's class.
CLASS HIERARCHY
Any Object::InsideOut class potentially has four categories of classes
associated with it:
1. Object::InsideOut
While the basis for all Object::InsideOut classes it is not an
object class per se because you can create objects from it (i.e.,
you can't do "Object::InsideOut-"new()>). While
"My::Class-"isa('Object::InsideOut')> will return true, because
Object::InsideOut is not an object class, it is not considered to
be part of a class's hierarchy.
2. The class itself
A class's hierarchy always includes itself.
3. Parent classes
These are all the Object::InsideOut classes up the inheritance tree
that a class is derived from.
4. Foreign classes
These are non-Object::InsideOut classes that a class inherits from.
(See "FOREIGN CLASS INHERITANCE" in Object::InsideOut.) Because of
implementation details, foreign classes do not appear in a class's
@ISA array. However, Object::InsideOut implements a version of
"->isa()" that handles foreign classes.
A class's hierarchy consists of any classes in the latter three
categories.
$meta->get_classes();
When called in an array context, returns a list that constitutes
the class hierarchy for the class or object used to generate the
metadata object. When called in a scalar context, returns an array
ref.
My::Class->isa();
$obj->isa();
When called in an array context, calling "->isa()" without any
arguments on an Object::InsideOut class or object returns a list of
the classes in the class hierarchy for that class or object, and is
equivalent to:
my @classes = $obj->meta()->get_classes();
When called in a scalar context, it returns an array ref containing
the classes.
CONSTRUCTOR PARAMETERS
Constructor parameters are the arguments given to a class's "->new()"
call.
$meta->get_args();
Returns a hash (hash ref in scalar context) containing information
on the parameters that can be used to construct an object from the
class associated with the metadata object. Here's an example of
such a hash:
{
'My::Class' => {
'data' => {
'field' => 1,
'type' => 'numeric',
},
'misc' => {
'mandatory' => 1,
},
},
'My::Parent' => {
'info' => {
'default' => '<none>',
},
},
}
The keys for this hash are the Object::IsideOut classes in the
class hierarchy. These class keys are paired with hash refs, the
keys of which are the names of the parameters for that class (e.g.,
'data' and 'misc' for My::Class, and 'info' for My::Parent). The
hashes paired to the parameters contain information about the
parameter:
field
The parameter corresponds directly to a class field, and is
automatically processed during object creation. See "Field-
Specific Parameters" in Object::InsideOut.
mandatory
The parameter is required for object creation. See "Mandatory
Parameters" in Object::InsideOut.
default
The default value assigned to the parameter if it is not found
in the arguments to "->new()". See "Default Values" in
Object::InsideOut.
preproc
The code ref for the subroutine that is used to preprocess a
parameter's value. See "Parameter Preprocessing" in
Object::InsideOut
type
The form of type checking performed on the parameter. See
"TYPE CHECKING" in Object::InsideOut for more details.
'numeric'
Parameter takes a numeric value as recognized by
Scalar::Util::looks_like_number().
'list'
'list(_subtype_)'
Parameter takes a single value (which is then placed in an
array ref) or an array ref.
When specified, the contents of the resulting array ref
must be of the specified subtype:
'numeric'
Same as for the basic type above.
A class name
Same as for the basic type below.
A reference type
Any reference type as returned by ref()).
'ARRAY(_subtype_)'
Parameter takes an array ref with contents of the specified
subtype as per the above.
A class name
Parameter takes an object of a specified class, or one of
its sub-classes as recognized by "->isa()".
Other reference type
Parameter takes a reference of the specified type as
returned by ref().
A code ref
Parameter takes a value that is type-checked by the code
ref paired to the 'type' key.
METHODS METADATA
The methods returned by a metadata object are those that are currently
available at the time of the "->get_methods()" call.
The presence of ":Automethod" subroutines in an Object::InsideOut
class, or "AUTOLOAD" in a foreign class means that the methods
supported by the class may not be determinable. The presence of
"AUTOLOAD" in the list of methods for a class should alert the
programmer to the fact that more methods may be supported than are
listed.
Methods that are excluded are private and hidden methods (see
"PERMISSIONS" in Object::InsideOut), methods that begin with an
underscore (which, by convention, means they are private), and
subroutines named "CLONE", "CLONE_SKIP", and "DESTROY" (which are not
methods). While technically a method, "import" is also excluded as it
is generally not invoked directly (i.e., it's usually called as part of
"use").
$meta->get_methods();
Returns a hash (hash ref in scalar context) containing information
on the methods for the class associated with the metadata object.
The keys in the hash are the method names. Paired to the names are
hash refs containing metadata about the methods. Here's an
example:
{
# Methods exported by Object::InsideOut
'new' => {
'class' => 'My::Class',
'kind' => 'constructor'
},
'clone' => {
'class' => 'My::Class',
'kind' => 'object'
},
'meta' => {
'class' => 'My::Class'
},
'set' => {
'class' => 'My::Class',
'kind' => 'object',
'restricted' => 1
},
# Methods provided by Object::InsideOut
'dump' => {
'class' => 'Object::InsideOut',
'kind' => 'object'
},
'pump' => {
'class' => 'Object::InsideOut',
'kind' => 'class'
},
'inherit' => {
'class' => 'Object::InsideOut',
'kind' => 'object',
'restricted' => 1
},
'heritage' => {
'class' => 'Object::InsideOut',
'kind' => 'object',
'restricted' => 1
},
'disinherit' => {
'class' => 'Object::InsideOut',
'kind' => 'object',
'restricted' => 1
},
# Methods generated by Object::InsideOut for My::Class
'set_data' => {
'class' => 'My::Class',
'kind' => 'set',
'type' => 'ARRAY',
'return' => 'new'
},
'get_data' => {
'class' => 'My::Class',
'kind' => 'get'
}
# Class method provided by My::Class
'my_method' => {
'class' => 'My::Class',
'kind' => 'class'
}
}
Here are the method metadata that are provided:
class
The class in whose symbol table the method resides. The method
may reside in the classes code, it may be exported by another
class, or it may be generated by Object::InsideOut.
Methods that are overridden in child classes are represented as
being associated with the most junior class for which they
appear.
kind
Designation of the characteristic of the method:
constructor
The "->new()" method, of course.
get, set or accessor
A get, set, or combined accessor generated by
Object::InsideOut. See "AcCESSOR GENERATION" in
Object::InsideOut.
cumulative, or cumulative (bottom up)
chained, or chained (bottom up)
A cumulative or chained method. See "CUMULATIVE METHODS"
in Object::InsideOut, and "CHAINED METHODS" in
Object::InsideOut. The class associated with these methods
is the most junior class in which they appears.
class
A method that is callable only on a class (e.g.,
"My::Class->my_method()").
object
A method that is callable only on a object (e.g.
"$obj->get_data()").
foreign
A subroutine found in a foreign class's symbol table.
Programmers must check the class's documentation to
determine which are actually methods, and what kinds of
methods they are.
overload
A subroutine used for object coercion. These may be called
as methods, but this is not normally how they are used.
automethod
Associated with an AUTOLOAD method for an Object::InsideOut
class that implements an ":Automethod" subroutine. See
"AUTOMETHODS" in Object::InsideOut.
type
The type checking that is done on arguments to set/combined
accessors generated by Object::InsideOut. See "TYPE CHECKING"
in Object::InsideOut
return
The value returned by a set/combined accessor generated by
Object::InsideOut. See "Set Accessor Return Value" in
Object::InsideOut
lvalue
The method is an :lvalue accessor.
restricted
The method is restricted (i.e., callable only from within the
class hierarchy; not callable from application code). See
"PERMISSIONS" in Object::InsideOut.
My::Class->can();
$obj->can();
When called in an array context, calling "->can()" without any
arguments on an Object::InsideOut class or object returns a list of
the method names for that class or object, and is equivalent to:
my %meths = $obj->meta()->get_methods();
my @methods = keys(%meths);
When called in a scalar context, it returns an array ref containing
the method names.
METADATA ATTRIBUTES
Class authors may add the ":Method" attribute to subroutines in their
classes to specifically designate them as OO-callable methods. If a
method is only a class method or only an object method, this may be
added as a parameter to the attribute:
sub my_method :Method(class)
{
...
The class or object parameter will appear in the metadata for the
method when listed using "->get_methods()".
CAUTION: Be sure not to use ":method" (all lowercase) except as
appropriate (see "ARGUMENT VALIDATION" in Object::InsideOut) as this is
a Perl reserved attribute.
The ":Sub" attribute can be used to designate subroutines that are not
OO-callable methods. These subroutines will not show up as part of the
methods listed by "->get_methods()", etc..
Subroutine names beginning with an underscore are, by convention,
considered private, and will not show up as part of the methods listed
by "->get_methods()", etc..
ADDING METADATA
Class authors may add additional metadata to their methods using the
"add_meta()" subroutine which is exported by this package. For
example, if the class implements it own ":lvalue" method, it should add
that metadata so that it is picked up the "->get_methods()":
package My::Class; {
use Object::InsideOut;
use Object::InsideOut::Metadata;
sub my_method :lvalue :Method(object)
{
....
}
add_meta(__PACKAGE__, 'my_method', 'lvalue', 1);
}
The arguments to "add_meta()" are:
Class name
This can usually be designated using the special literal
C__PACKAGE__>.
Method name
Metadata name
This can be any of the metadata names under "METHODS METADATA", or
can be whatever additional name the programmer chooses to
implement.
Metadata value
When adding multiple metadata for a method, they may be enclosed in a
single hash ref:
add_meta(__PACKAGE__, 'my_method', { 'lvalue' => 1,
'return' => 'old' });
If adding metadata for multiple methods, another level of hash may be
used:
add_meta(__PACKAGE__, { 'my_method' => { 'lvalue' => 1,
'return' => 'old' },
'get_info' => { 'my_meta' => 'true' } });
TO DO
Provide filtering capabilities on the method information returned by
"->get_methods()".
REQUIREMENTS
Perl 5.8.0 or later
SEE ALSO
Object::InsideOut
Perl 6 introspection:
<http://dev.perl.org/perl6/doc/design/apo/A12.html#Introspection>, and
<http://dev.perl.org/perl6/rfc/335.html>
AUTHOR
Jerry D. Hedden, <jdhedden AT cpan DOT org>
COPYRIGHT AND LICENSE
Copyright 2006 - 2009 Jerry D. Hedden. All rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.14.1 2011-03-22 Object::InsideOut::Metadata(3)
