Provided by: librose-object-perl_0.860-2_all 
NAME
Rose::Object::MakeMethods - A simple method maker base class.
SYNOPSIS
package MyMethodMaker;
use Rose::Object::MakeMethods;
our @ISA = qw(Rose::Object::MakeMethods);
sub widget
{
my($class, $name, $args) = @_;
my $key = $args->{'hash_key'} || $name;
my $interface = $args->{'interface'} || 'get_set';
my %methods;
if($interface =~ /^get_set/)
{
$methods{$name} = sub
{
my($self) = shift;
if(@_) { ... }
...
return $self->{$key};
};
}
if($interface eq 'get_set_delete')
{
$methods{"delete_$name"} = sub { ... };
)
return \%methods;
}
...
package MyObject;
sub new { ... }
use MyMethodMaker
(
'widget --get_set_delete' => 'foo',
'widget' =>
[
'bar',
'baz',
]
);
...
$o = MyObject->new;
$o->foo($bar);
$o->delete_foo();
print $o->bar . $o->baz;
...
DESCRIPTION
Rose::Object::MakeMethods is the base class for a family of method makers. A method maker
is a module that's used to define methods in other packages. The actual method makers are
subclasses of Rose::Object::MakeMethods that define the names and options of the different
kinds of methods that they can make.
There are method makers that make both object methods and class methods. The object method
makers are in the "Rose::Object::MakeMethods::*" namespace. The class method makers are in
the "Rose::Class::MakeMethods::*" namespace for the sake of clarity, but still inherit
from Class::MethodMaker and therefore share the same method making interface.
Several useful method makers are included under the "Rose::Object::MakeMethods::*" and
"Rose::Class::MakeMethods::*" namespaces, mostly for use by other "Rose::*" objects and
classes.
This family of modules is not as powerful or flexible as the one that inspired it:
Class::MethodMaker. I found that I was only using a tiny corner of the functionality
provided by Class::MethodMaker, so I wrote this as a simple, smaller replacement.
The fact that many "Rose::*" modules use Rose::Object::MakeMethods subclasses to make
their methods should be considered an implementation detail that can change at any time.
CLASS METHODS
allow_apparent_reload [BOOL]
Get or set an attribute that determines whether or not to allow an attempt to re-make
the same method using the same class that made it earlier. The default is true.
This issue comes up when a module is forcibly reloaded, e.g., by Apache::Reload or
Apache::StatINC. When this happens, all the "make methods" actions will be attempted
again. In the absence of the "preserve_existing" or "override_existing" options, the
allow_apparent_reload attribute will be consulted. If it's true, and if it appears
that the method in question was made by this method-maker class, then it behaves as if
the "preserve_existing" option had been passed. If it is false, then a fatal "method
redefined" error will occur.
import SPEC
The "import" class method is mean to be called implicitly as a result of a "use"
statement. For example:
use Rose::Object::MakeMethods::Generic
(
SPEC
);
is roughly equivalent to:
require Rose::Object::MakeMethods::Generic;
Rose::Object::MakeMethods::Generic->import(SPEC);
where SPEC is a series of specifications for the methods to be created. (But don't
call import explicitly; use make_methods instead.)
In response to each method specification, one or more methods are created.
The first part of the SPEC argument is an optional hash reference whose contents are
intended to modify the behavior of the method maker class itself, rather than the
individual methods being made. There are currently only two valid arguments for this
hash:
target_class CLASS
Specifies that class that the methods will be added to. Defaults to the class
from which the call was made. For example, this:
use Rose::Object::MakeMethods::Generic
(
{ target_class => 'Foo' },
...
);
Is equivalent to this:
package Foo;
use Rose::Object::MakeMethods::Generic
(
...
);
In general, the "target_class" argument is omitted since methods are usually
indented to end up in the class of the caller.
override_existing BOOL
By default, attempting to create a method that already exists will result in a
fatal error. But if the "override_existing" option is set to a true value, the
existing method will be replaced with the generated method.
preserve_existing BOOL
By default, attempting to create a method that already exists will result in a
fatal error. But if the "preserve_existing" option is set to a true value, the
existing method will be left unmodified. This option takes precedence over the
"override_existing" option.
After the optional hash reference full off options intended for the method maker class
itself, a series of method specifications should be provided. Each method
specification defines one or more named methods. The components of such a
specification are:
• The Method Type
This is the name of the subroutine that will be called in order to generated the
methods (see SUBCLASSING for more information). It describes the nature of the
generated method. For example, "scalar", "array", "bitfield", "object"
• Method Type Arguments
Name/value pairs that are passed to the method maker of the specified type in
order to modify its behavior.
• Method Names
One or more names for the methods that are to be created. Note that a method
maker of a particular type may choose to modify or ignore these names. In the
common case, for each method name argument, a single method is created with the
same name as the method name argument.
Given the method type "bitfield" and the method arguments "opt1" and "opt2", the
following examples show all valid forms for method specifications, with equivalent
forms grouped together.
Create a bitfield method named "my_bits":
bitfield => 'my_bits'
bitfield => [ 'my_bits' ],
bitfield => [ 'my_bits' => {} ],
Create a bitfield method named "my_bits", passing the "opt1" argument with a value of
2.
'bitfield --opt1=2' => 'my_bits'
'bitfield --opt1=2' => [ 'my_bits' ]
bitfield => [ 'my_bits' => { opt1 => 2 } ]
Create a bitfield method named "my_bits", passing the "opt1" argument with a value of
2 and the "opt2" argument with a value of 7.
'bitfield --opt1=2 --opt2=7' => 'my_bits'
'bitfield --opt1=2 --opt2=7' => [ 'my_bits' ]
bitfield => [ 'my_bits' => { opt1 => 2, opt2 => 7 } ]
'bitfield --opt2=7' => [ 'my_bits' => { opt1 => 2 } ]
In the case of a conflict between the options specified with the "--name=value" syntax
and those provided in the hash reference, the ones in the hash reference take
precedence. For example, these are equivalent:
'bitfield --opt1=99' => 'my_bits'
'bitfield --opt1=5' => [ 'my_bits' => { opt1 => 99 } ]
If no value is provided for the first option, and if it is specified using the
"--name" syntax, then it is taken as the value of the "interface" option. That is,
this:
'bitfield --foobar' => 'my_bits'
is equivalent to these:
'bitfield --interface=foobar' => 'my_bits'
bitfield => [ my_bits => { interface => 'foobar' } ]
This shortcut supports the convention that the "interface" option is used to decide
which set of methods to create. But it's just a convention; the "interface" option is
no different from any of the other options when it is eventually passed to the method
maker of a given type.
Any option other than the very first that is specified using the "--name" form and
that lacks an explicit value is simply set to 1. That is, this:
'bitfield --foobar --baz' => 'my_bits'
is equivalent to these:
'bitfield --interface=foobar --baz=1' => 'my_bits'
bitfield =>
[
my_bits => { interface => 'foobar', baz => 1 }
]
Multiple method names can be specified simultaneously for a given method type and set
of options. For example, to create methods named "my_bits[1-3]", all of the same type
and with the same options, any of these would work:
'bitfield --opt1=2' =>
[
'my_bits1',
'my_bits2',
'my_bits3',
]
bitfield =>
[
'my_bits1' => { opt1 => 2 },
'my_bits2' => { opt1 => 2 },
'my_bits3' => { opt1 => 2 },
]
When options are provided using the "--name=value" format, they apply to all methods
listed inside the array reference, unless overridden. Here's an example of an
override:
'bitfield --opt1=2' =>
[
'my_bits1',
'my_bits2',
'my_bits3' => { opt1 => 999 },
]
In this case, "my_bits1" and "my_bits2" use "opt1" values of 2, but "my_bits3" uses an
"opt1" value of 999. Also note that it's okay to mix bare method names ("my_bits1"
and "my_bits2") with method names that have associated hash reference options
("my_bits3"), all inside the same array reference.
Finally, putting it all together, here's a full example using several different
formats.
use Rose::Object::MakeMethods::Generic
(
{ override_existing => 1 },
'bitfield' => [ qw(my_bits other_bits) ],
'bitfield --opt1=5' =>
[
'a',
'b',
],
'bitfield' =>
[
'c',
'd' => { opt2 => 7 },
'e' => { opt1 => 1 },
'f' => { }, # empty is okay too
]
);
In the documentation for the various Rose::Object::MakeMethods subclasses, any of the
valid forms may be used in the examples.
make_methods SPEC
This method is equivalent to the "import" method, but makes the intent of the code
clearer when it is called explicitly. (The "import" method is only meant to be called
implicitly by "use".)
SUBCLASSING
In order to make a Rose::Object::MakeMethods subclass that can actually make some methods,
simply subclass Rose::Object::MakeMethods and define one subroutine for each method type
you want to support.
The subroutine will be passed three arguments when it is called:
• The class of the method maker as a string. This argument is usually ignored unless
you are going to call some other class method.
• The method name. In the common case, a single method with this name is defined, but
you are free to do whatever you want with it, including ignoring it.
• A reference to a hash containing the options for the method.
The subroutine is expected to return a reference to a hash containing name/code reference
pairs. Note that the subroutine does not actually install the methods. It simple returns
the name of each method that is to be installed, along with references to the closures
that contain the code for those methods.
This subroutine is called for each name in the method specifier. For example, this would
result in three separate calls to the "bitfield" subroutine of the "MyMethodMaker" class:
use MyMethodMaker
(
bitfield =>
[
'my_bits',
'your_bits' => { size => 32 },
'other_bits' => { size => 128 },
]
);
So why not have the subroutine return a single code reference rather than a reference to a
hash of name.code reference pairs? There are two reasons.
First, remember that the name argument ("my_bits", "your_bits", "other_bits") may be
modified or ignored by the method maker. The actual names of the methods created are
determined by the keys of the hash reference returned by the subroutine.
Second, a single call with a single method name argument may result in the creation more
than one method--usually a "family" of methods. For example:
package MyObject;
use MyMethodMaker
(
# creates add_book(), delete_book(), and books() methods
'hash --manip' => 'book',
);
...
$o = MyObject->new(...);
$o->add_book($book);
print join("\n", map { $_->title } $o->books);
$o->delete_book($book);
Here, the "hash" method type elected to create three methods by prepending "add_" and
"delete_" and appending "s" to the supplied method name argument, "book".
Anything not specified in this documentation is simply a matter of convention. For
example, the Rose::Object::MakeMethods subclasses all use a common set of method options:
"hash_key", "interface", etc. As you read their documentation, this will become apparent.
Finally, here's an example of a subclass that makes scalar accessors:
package Rose::Object::MakeMethods::Generic;
use strict;
use Carp();
use Rose::Object::MakeMethods;
our @ISA = qw(Rose::Object::MakeMethods);
sub scalar
{
my($class, $name, $args) = @_;
my %methods;
my $key = $args->{'hash_key'} || $name;
my $interface = $args->{'interface'} || 'get_set';
if($interface eq 'get_set_init')
{
my $init_method = $args->{'init_method'} || "init_$name";
$methods{$name} = sub
{
return $_[0]->{$key} = $_[1] if(@_ > 1);
return defined $_[0]->{$key} ? $_[0]->{$key} :
($_[0]->{$key} = $_[0]->$init_method());
}
}
elsif($interface eq 'get_set')
{
$methods{$name} = sub
{
return $_[0]->{$key} = $_[1] if(@_ > 1);
return $_[0]->{$key};
}
}
else { Carp::croak "Unknown interface: $interface" }
return \%methods;
}
It can be used like this:
package MyObject;
use Rose::Object::MakeMethods::Generic
(
scalar =>
[
'power',
'error',
],
'scalar --get_set_init' => 'name',
);
sub init_name { 'Fred' }
...
$o = MyObject->new(power => 5);
print $o->name; # Fred
$o->power(99) or die $o->error;
This is actually a subset of the code in the actual Rose::Object::MakeMethods::Generic
module. See the rest of the "Rose::Object::MakeMethods::*" and
"Rose::Class::MakeMethods::*" modules for more examples.
AUTHOR
John C. Siracusa (siracusa@gmail.com)
LICENSE
Copyright (c) 2010 by John C. Siracusa. All rights reserved. This program is free
software; you can redistribute it and/or modify it under the same terms as Perl itself.