Provided by: libclass-makemethods-perl_1.01-7_all 
NAME
Class::MakeMethods::Template - Extensible code templates
SYNOPSIS
package MyObject;
use Class::MakeMethods::Template::Hash (
'new' => 'new',
'string' => 'foo',
'number' => 'bar',
);
my $obj = MyObject->new( foo => "Foozle", bar => 23 );
print $obj->foo();
$obj->bar(42);
MOTIVATION
If you compare the source code of some of the closure-generating methods provided by other
subclasses of Class::MakeMethods, such as the "hash" accessors provided by the various
Standard::* subclasses, you will notice a fair amount of duplication. This module provides
a way of assembling common pieces of code to facilitate support the maintenance of much
larger libraries of generated methods.
DESCRIPTION
This module extends the Class::MakeMethods framework by providing an abstract superclass
for extensible code-templating method generators.
Common types of methods are generalized into template definitions. For example,
"Template::Generic"'s "new" provides a template for methods that create object instances,
while "Template::Generic"'s "scalar" is a template for methods that allow you to get and
set individual scalar values.
Thse definitions are then re-used and modified by various template subclasses. For
example, the "Template::Hash" subclass supports blessed-hash objects, while the
"Template::Global" subclass supports shared data; each of them includes an appropriate
version of the "scalar" accessor template for those object types.
Each template defines one or more behaviors, individual methods which can be installed in
a calling package, and interfaces, which select from those behaviours and indicate the
names to install the methods under.
Each individual meta-method defined by a calling package requires a method name, and may
optionally include other key-value parameters, which can control the operation of some
meta-methods.
USAGE
Class::MakeMethods Calling Conventions
When you "use" this package, the method declarations you provide as arguments cause
subroutines to be generated and installed in your module.
You can also omit the arguments to "use" and instead make methods at runtime by passing
the declarations to a subsequent call to "make()".
You may include any number of declarations in each call to "use" or "make()". If methods
with the same name already exist, earlier calls to "use" or "make()" win over later ones,
but within each call, later declarations superceed earlier ones.
You can install methods in a different package by passing "-TargetClass => package" as
your first arguments to "use" or "make".
See Class::MakeMethods for more details.
Passing Parameters
The following types of Basic declarations are supported:
• generator_type => "method_name"
• generator_type => "name_1 name_2..."
• generator_type => [ "name_1", "name_2", ...]
See "TEMPLATE CLASSES" in Class::MakeMethods::Docs::Catalog for a list of the supported
values of generator_type.
For each method name you provide, a subroutine of the indicated type will be generated and
installed under that name in your module.
Method names should start with a letter, followed by zero or more letters, numbers, or
underscores.
Standard Declaration Syntax
The Standard syntax provides several ways to optionally associate a hash of additional
parameters with a given method name.
• generator_type => [ "name_1" => { param=>value... }, ... ]
A hash of parameters to use just for this method name.
(Note: to prevent confusion with self-contained definition hashes, described below,
parameter hashes following a method name must not contain the key 'name'.)
• generator_type => [ [ "name_1", "name_2", ... ] => { param=>value... } ]
Each of these method names gets a copy of the same set of parameters.
• generator_type => [ { "name"=>"name_1", param=>value... }, ... ]
By including the reserved parameter "name", you create a self contained declaration
with that name and any associated hash values.
Basic declarations, as described above, are treated as having an empty parameter hash.
Default Parameters
A set of default parameters to be used for several declarations may be specified using any
of the following types of arguments to a Template method generator call:
• '-param' => 'value'
Set a default value for the specified parameter.
• '--' => { 'param' => 'value', ... }
Set default values for one or more parameters. Equivalent to a series of '-param' =>
'value' pairs for each pair in the referenced hash.
• '--special_param_value'
Specifies a value for special parameter; the two supported parameter types are:
- '--interface_name'
Select a predefined interface; equivalent to '-interface'=> 'interface_name'.
For more information about interfaces, see "Selecting Interfaces" below.
- '--modifier_name'
Select a global behavior modifier, such as '--private' or '--protected'.
For more information about modifiers, see "Selecting Modifiers" below.
Parameters set in these ways are passed to each declaration that follows it until the end
of the method-generator argument array, or until overridden by another declaration.
Parameters specified in a hash for a specific method name, as discussed above, will
override the defaults of the same name for that particular method.
PARAMETER REFERENCE
Each meta-method is allocated a hash in which to store its parameters and optional
information.
(Note that you can not override parameters on a per-object level.)
Special Parameters
The following parameters are pre-defined or have a special meaning:
• name
The primary name of the meta-method. Note that the subroutines installed into the
calling package may be given different names, depending on the rules specified by the
interface.
• interface
The name of a predefined interface, or a reference to a custom interface, to use for
this meta-method. See "Selecting Interfaces", below.
• modifier
The names of one or more predefined modifier flags. See "Selecting Modifiers", below.
Informative Parameters
The following parameters are set automatically when your meta-method is declared:
• target_class
The class that requested the meta-method, into which its subroutines will be
installed.
• template_name
The Class::MakeMethods::Template method used for this declaration.
• template_class
The Class::MakeMethods::Template subclass used for this declaration.
Other Parameters
Specific subclasses and template types provide support for additional parameters.
Note that you generally should not arbitrarily assign additional parameters to a meta-
method unless you know that they do not conflict with any parameters already defined or
used by that meta-method.
Parameter Expansion
If a parameter specification contains '*', it is replaced with the primary method name.
Example: The following defines counter (*, *_incr, *_reset) meta-methods j and k, which
use the hash keys j_index and k_index to fetch and store their values.
use Class::MakeMethods::Template::Hash
counter => [ '-hash_key' => '*_index', qw/ j k / ];
(See Class::MakeMethods::Template::Hash for information about the "hash_key" parameter.)
If a parameter specification contains '*{param}', it is replaced with the value of that
parameter.
Example: The following defines a Hash scalar meta-method which will store its value in a
hash key composed of the defining package's name and individual method name, such as
"$self->{MyObject-foo}":
use Class::MakeMethods::Template::Hash
'scalar' => [ '-hash_key' => '*{target_class}-*{name}', qw/ l / ];
Selecting Interfaces
Each template provides one or more predefined interfaces, each of which specifies one or
more methods to be installed in your package, and the method names to use. Check the
documentation for specific templates for a list of which interfaces they define.
An interface may be specified for a single method by providing an 'interface' parameter:
• 'interface_name'
Select a predefined interface.
Example: Instead of the normal Hash scalar method named x, the following creates
methods with "Java-style" names and behaviors, getx and setx.
use Class::MakeMethods::Template::Hash
'scalar' => [ 'x' => { interface=>'java' } ];
(See "scalar" in Class::MakeMethods::Template::Generic for a description of the "java"
interface.)
• 'behavior_name'
A simple interface consisting only of the named behavior.
For example, the below declaration creates a read-only methods named q. (There are no
set or clear methods, so any value would have to be placed in the hash by other
means.)
use Class::MakeMethods::Template::Hash (
'scalar' => [ 'q' => { interface=>'get' } ]
);
• { 'subroutine_name_pattern' => 'behavior_name', ... }
A custom interface consists of a hash-ref that maps subroutine names to the associated
behaviors. Any "*" characters in subroutine_name_pattern are replaced with the
declared method name.
For example, the below delcaration creates paired get_w and set_w methods:
use Class::MakeMethods::Template::Hash (
'scalar' => [ 'w' => { interface=> { 'get_*'=>'get', 'set_*'=>'set' } } ]
);
Some interfaces provide very different behaviors than the default interface.
Example: The following defines a method g, which if called with an argument appends to,
rather than overwriting, the current value:
use Class::MakeMethods::Template::Hash
'string' => [ '--get_concat', 'g' ];
A named interface may also be specified as a default in the argument list with a leading
'--' followed by the interface's name.
Example: Instead of the normal Hash scalar methods (named x and clear_x), the following
creates methods with "Java-style" names and behaviors (getx, setx).
use Class::MakeMethods::Template::Hash
'scalar' => [ '--java', 'x' ];
An interface set in this way affects all meta-methods that follow it until another
interface is selected or the end of the array is reached; to return to the original names
request the 'default' interface.
Example: The below creates "Java-style" methods for e and f, "normal scalar" methods for
g, and "Eiffel-style" methods for h.
use Class::MakeMethods::Template::Hash
'scalar' => [
'--java'=> 'e', 'f',
'--default'=> 'g',
'--eiffel'=> 'h',
];
Selecting Modifiers
You may select modifiers, which will affect all behaviors.
use Class::MakeMethods::Template::Hash
'scalar' => [ 'a', '--protected' => 'b', --private' => 'c' ];
Method b croaks if it's called from outside of the current package or its subclasses.
Method c croaks if it's called from outside of the current package.
See the documentation for each template to learn which modifiers it supports.
Runtime Parameter Access
If the meta-method is defined using an interface which includes the attributes method,
run-time access to meta-method parameters is available.
Example: The following defines a counter meta-method named y, and then later changes the
'join' parameter for that method at runtime.
use Class::MakeMethods ( get_concat => 'y' );
y_attributes(undef, 'join', "\t" )
print y_attributes(undef, 'join')
EXTENDING
You can create your own method-generator templates by following the below outline.
Mechanisms
Dynamic generation of methods in Perl generally depends on one of two approaches: string
evals, which can be as flexible as your string-manipulation functions allow, but are run-
time resource intensive; or closures, which are limited by the number of subroutine
constructors you write ahead of time but which are faster and smaller than evals.
Class::MakeMethods::Template uses both of these approaches: To generate different types of
subroutines, a simple text-substitution mechanism combines bits of Perl to produce the
source code for a subroutine, and then evals those to produce code refs. Any differences
which can be handled with only data changes are managed at the closure layer; once the
subroutines are built, they are repeatedly bound as closures to hashes of parameter data.
Code Generation
A substitution-based "macro language" is used to assemble code strings. This happens only
once per specific subclass/template/behavior combination used in your program. (If you
have disk-caching enabled, the template interpretation is only done once, and then saved;
see below.)
There are numerous examples of this within the Generic interface and its subclasses; for
examples, look at the following methods: Universal:generic, Generic:scalar, Hash:generic,
and Hash:scalar.
See Class::MakeMethods::Utility::TextBuilder for more information.
Template Definitions
Template method generators are declared by creating a subroutine that returns a hash-ref
of information about the template. When these subroutines are first called, the template
information is filled in with imported and derived values, blessed as a
Class::MakeMethods::Template object, and cached.
Each "use" of your subclass, or call to its "make", causes these objects to assemble the
requested methods and return them to Class::MakeMethods for installation in the calling
package.
Method generators defined this way will have support for parameters, custom interfaces,
and the other features discussed above.
(Your module may also use the "Aliasing" and "Rewriting" functionality described in
"EXTENDING" in Class::MakeMethods.)
Definition hashes contain several types of named resources in a second level of hash-refs
under the following keys:
• interface - Naming styles (see "Defining Interfaces", below)
• params - Default parameters for meta-methods declared with this template (see "Default
Parameters", below)
• behavior - Method recipes (see "Defining Behaviors", below)
• code_expr - Bits of code used by the behaviors
Minimum Template Definition
You must at least specify one behavior; all other information is optional.
Class::MakeMethods will automatically fill in the template name and class as
'template_name' and 'template_class' entries in the version of your template definition
hash that it caches and uses for future execution.
For example a simple sub-class that defines a method type upper_case_get_set might look
like this:
package Class::MakeMethods::UpperCase;
use Class::MakeMethods '-isasubclass';
sub uc_scalar {
return {
'behavior' => {
'default' => sub {
my $m_info = $_[0];
return sub {
my $self = shift;
if ( scalar @_ ) {
$self->{ $m_info->{'name'} } = uc( shift )
} else {
$self->{ $m_info->{'name'} };
}
}
},
}
}
}
And a caller could then use it to generate methods in their package by invoking:
Class::MakeMethods::UpperCase->make( 'uc_scalar' => [ 'foo' ] );
Default Parameters
Each template may include a set of default parameters for all declarations as "params =>
hash_ref".
Template-default parameters can be overridden by interface '-params', described below, and
and method-specific parameters, described above.
Defining Interfaces
Template definitions may have one or more interfaces, including the default one, named
'default', which is automatically selected if another interface is not requested. (If no
default interface is provided, one is constructed, which simply calls for a behavior named
default.)
Most commonly, an interface is specified as a hash which maps one or more subroutine names
to the behavior to use for each. The interface subroutine names generally contain an
asterisk character, '*', which will be replaced by the name of each meta-method.
Example: The below defines methods e_get, e_set, and e_clear.
use Class::MakeMethods::Template::Hash
'scalar' => [
-interface=>{ '*_clear'=>clear, '*_get'=>'get', '*_set'=>'set' }, 'e'
];
If the provided name does not contain an asterisk, it will not be modified for individual
meta-methods; for examples, see the bit_fields method generated by Generic bits, and the
DESTROY method generated by InsideOut meta-methods.
In addition to the name-to-behavior correspondences described above, interfaces may also
contain additional entries with keys beginning with the '-' character which are
interpreted as follows:
• "-params => hash_ref"
Interfaces may include a '-params' key and associated reference to a hash of default
parameters for that interface.
• "-base => interface_name"
Interfaces can be based on previously existing ones by including a -base specification
in the the hash. The base value should contain one or more space-separated names of
the interfaces to be included.
Example: The below defines methods getG, setG, and clearG.
use Class::MakeMethods::Template::Hash
'scalar' => [
-interface => { -base=>'java', 'clear*'=>'clear' }, qw/ G /
];
If multiple interfaces are included in the -base specification and specify different
behaviors for the same subroutine name, the later ones will override the earlier.
Names which appear in the base interface can be overridden by providing a new value,
or a name can be removed by mapping it to undef or the empty string.
Example: The following defines a get-set meta-method h, but suppresses the clear_h
method:
use Class::MakeMethods::Template::Hash
'scalar' => [
-interface => { -base=>'with_clear', 'clear_*'=>'' }, qw/ h /
];
Defining Behaviors
Behaviors can be provided as text which is eval'd to form a closure-generating subroutine
when it's first used; $self is automatically defined and assigned the value of the first
argument.
'behavior' => {
'default' => q{
if ( scalar @_ ) { $self->{ $m_info->{'name'} } = uc shift }
$self->{ $m_info->{'name'} };
},
}
A simple substitution syntax provides for macro interpretation with definition strings.
This functionality is currently undocumented; for additional details see the
_interpret_text_builder function in Class::MakeMethods, and review the code_expr hashes
defined in Class::MakeMethods::Generic.
Importing
You can copy values out of other template definitions by specifying an '-import' key and
corresponding hash reference. You can specify an -import for inside any of the template
definition sub-hashes. If no -import is specified for a subhash, and there is a top-level
-import value, it is used instead.
Inside an -import hash, provide "TemplateClass:type" names for each source you wish to
copy from, and the values to import, which can be a string, a reference to an array of
strings, or '*' to import everything available. (The order of copying is not defined.)
Example: The below definition creates a new template which is identical to an existing
one.
package Class::MakeMethods::MyMethods;
sub scalarama {
{ -import => { 'Template::Hash:scalar' => '*' } }
}
Values that are already set are not modified, unless they're an array ref, in which case
they're added to.
Example:
package Class::MakeMethods::MyMethods;
sub foo_method {
{ 'behavior' => {
'-init' => [ sub { warn "Defining foo_method $_[0]->{'name'}" } ],
'default' => q{ warn "Calling foo_method behavior" }.
} }
}
sub bar_method {
{ 'behavior' => {
-import => { 'MyMethods:foo_method' => '*' },
'-init' => [ sub { warn "Defining bar_method $_[0]->{'name'}" } ],
'default' => q{ warn "Calling bar_method behavior" }.
} }
}
In this case, the bar_method ends up with an array of two '-init' subroutines, its own and
the imported one, but only its own default behavior.
Modifying Existing Templates
You can over-write information contained in template definitions to alter their subsequent
behavior.
Example: The following extends the Hash:scalar template definition by adding a new
interface, and then uses it to create scalar accessor methods named access_p and access_q
that get and set values for the hash keys 'p' and 'q':
Class::MakeMethods::Template::Hash->named_method('scalar')->
{'interface'}{'frozzle'} = { 'access_*'=>'get_set' };
package My::Object;
Class::MakeMethods::Template::Hash->make( 'scalar' => [ --frozzle => qw( p q ) ] );
$object->access_p('Potato'); # $object->{p} = 'Potato'
print $object->access_q(); # print $object->{q}
Note that this constitutes "action at a distance" and will affect subsequent use by other
packages; unless you are "fixing" the current behavior, you are urged to create your own
template definition which imports the base behavior of the existing template and overrides
the information in question.
Example: The following safely declares a new version of Hash:scalar with the desired
additional interface:
package My::Methods;
sub scalar {
{
-import => { 'Template::Hash:scalar' => '*' } ,
interface => { 'frozzle' => { 'access_*'=>'get_set' } },
}
}
package My::Object;
My::Methods->make( 'scalar' => [ --frozzle => qw( p q ) ] );
Disk Caching
To enable disk caching of generated code, create an empty directory and pass it to the
DiskCache package:
use Class::MakeMethods::Utility::DiskCache qw( /my/code/dir );
This has a mixed effect on performance, but has the notable advantage of letting you view
the subroutines that are being generated by your templates.
See Class::MakeMethods::Utility::DiskCache for more information.
SEE ALSO
See Class::MakeMethods for general information about this distribution.
See Class::MakeMethods::Examples for some illustrations of what you can do with this
package.
For distribution, installation, support, copyright and license information, see
Class::MakeMethods::Docs::ReadMe.