NAME
"Module::PluginFinder" - automatically choose the most appropriate
plugin module.
SYNOPSIS
use Module::PluginFinder;
my $finder = Module::PluginFinder->new(
search_path => 'MyApp::Plugin',
filter => sub {
my ( $module, $searchkey ) = @_;
$module->can( $searchkey );
},
);
my $ball = $finder->construct( "bounce" );
$ball->bounce();
my $fish = $finder->construct( "swim" );
$fish->swim();
DESCRIPTION
This module provides a factory class. Objects in this class search for a
specific plugin module to fit some criteria. Each time a new object is
to be constructed by the factory, the caller should provide a value
which in some way indicates the kind of object required. The factory's
filter function is then used to determine which plugin module fits the
criteria.
The most flexible way to determine the required module is to provide a
filter function. When looking for a suitable module, the function is
called once for each candidate module, and is passed the module's name
and the search key. The function can then return a boolean to indicate
whether the module will be suitable. The value of the search key is not
directly used by the "Module::PluginFinder" in this case, and therefore
is not restricted to being a simple scalar value; any sort of reference
may be passed.
Instead of a filter function, the factory can inspect a package variable
or constant method in each of the candidate modules, looking for a
string match with the search key; see the "typevar" and "typefunc"
constructor arguments. When using this construction, a map from type
names to module names will be cached at the time the
"Module::PluginFinder" object is created, and will therefore not be
sensitive to changes in the values once this is done. Because of this,
the key should be a simple string, rather than a reference.
CONSTRUCTOR
$finder = Module::PluginFinder->new( %args )
Constructs a new "Module::PluginFinder" factory object. The constructor
will search the module path for all available plugins, as determined by
the "search_path" key and store them.
The %args hash must take the following keys:
search_path => STRING or ARRAY
A string declaring the module namespace, or an array reference
of module namespaces to search for plugins (passed to
Module::Pluggable::Object).
In order to specify the way candidate modules are selected, one of the
following keys must be supplied.
filter => CODE
The filter function for determining whether a module is suitable
as a plugin
typevar => STRING
The name of a package variable to match against the search key
typefunc => STRING
The name of a package method to call to return the type name.
The method will be called in scalar context with no arguments;
as
$type = $module->$typefunc();
If it returns "undef" or throws an exception, then the module
will be ignored
METHODS
@modules = $finder->modules()
Returns the list of module names available to the finder.
$module = $finder->find_module( $searchkey )
Search for a plugin module that matches the search key. Returns the name
of the first module for which the filter returns true, or "undef" if no
suitable module was found.
$searchkey
A value to pass to the stored filter function.
$object = $finder->construct( $searchkey, @constructorargs )
Search for a plugin module that matches the search key, then attempt to
create a new object in that class. If a suitable module is found to
match the $searchkey then the "new" method is called on it, passing the
@constructorargs. If no suitable module is found then an exception is
thrown.
$searchkey
A value to pass to the stored filter function.
@constructorargs
A list to pass to the class constructor.
$finder->rescan()
Perform another search for plugin modules. This method is useful
whenever new modules may be present since the object was first
constructed.
EXAMPLES
The filter function allows various ways to select plugin modules on
different criteria. The following examples indicate a few ways to do
this.
Availability of a function / method
my $f = Module::PluginFinder->new(
search_path => ...,
filter => sub {
my ( $module, $searchkey ) = @_;
return $module->can( $searchkey );
},
);
Each plugin then simply has to implement the required function or method
in order to be automatically selected.
Value of a method call
my $f = Module::PluginFinder->new(
search_path => ...,
filter => sub {
my ( $module, $searchkey ) = @_;
return 0 unless $module->can( "is_plugin_for" );
return $module->is_plugin_for( $searchkey );
},
);
Each plugin then needs to implement a method called "is_plugin_for",
that should examine the $searchkey and perform whatever testing it
requires, then return a boolean to indicate if the plugin is suitable.
Value of a constant
Because a constant declared by the "use constant" pragma is a plain
function, it can be called by the "typefunc" filter:
my $f = Module::PluginFinder->new(
search_path => ...,
typefunc => 'PLUGIN_TYPE',
);
Each plugin can then declare its type using a constuction like
use constant PLUGIN_TYPE => "my type here";
Alternatively, a normal package method may be created that performs any
work required to determine the plugin's type
sub PLUGIN_TYPE
{
my $class = shift;
...
return $typename;
}
Note that the type function in each module will only be called once, and
the returned value cached.
Value of a package scalar
The "typevar" constructor argument generates the filter function
automatically.
my $f = Module::PluginFinder->new(
search_path => ...,
typevar => 'PLUGIN_TYPE',
);
Each plugin can then declare its type using a normal "our" scalar
variable:
our $PLUGIN_TYPE = "my type here";
SEE ALSO
* Module::Pluggable - automatically give your module the ability to
have plugins
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>