Class::MakeMethods::Template - Extensible code templates
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);
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.
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.
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.
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.
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.
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.
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.)
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.
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.
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.
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 / ];
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',
];
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.
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')
You can create your own method-generator templates by following the below
outline.
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.
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 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
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' ] );
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.
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 /
];
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.
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.
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 ) ] );
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 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.