Module::ImplementationUser Contributed Perl DocumentaModule::Implementation(3)NAMEModule::Implementation - Loads one of several alternate underlying
implementations for a module
VERSION
version 0.07
SYNOPSIS
package Foo::Bar;
use Module::Implementation;
BEGIN {
my $loader = Module::Implementation::build_loader_sub(
implementations => [ 'XS', 'PurePerl' ],
symbols => [ 'run', 'check' ],
);
$loader->();
}
package Consumer;
# loads the first viable implementation
use Foo::Bar;
DESCRIPTION
This module abstracts out the process of choosing one of several
underlying implementations for a module. This can be used to provide XS
and pure Perl implementations of a module, or it could be used to load
an implementation for a given OS or any other case of needing to
provide multiple implementations.
This module is only useful when you know all the implementations ahead
of time. If you want to load arbitrary implementations then you
probably want something like a plugin system, not this module.
API
This module provides two subroutines, neither of which are exported.
Module::Implementation::build_loader_sub(...)
This subroutine takes the following arguments.
· implementations
This should be an array reference of implementation names. Each
name should correspond to a module in the caller's namespace.
In other words, using the example in the "SYNOPSIS", this module
will look for the "Foo::Bar::XS" and "Foo::Bar::PurePerl" modules.
This argument is required.
· symbols
A list of symbols to copy from the implementation package to the
calling package.
These can be prefixed with a variable type: "$", "@", "%", "&", or
"*)". If no prefix is given, the symbol is assumed to be a
subroutine.
This argument is optional.
This subroutine returns the implementation loader as a sub reference.
It is up to you to call this loader sub in your code.
I recommend that you do not call this loader in an "import()" sub. If a
caller explicitly requests no imports, your "import()" sub will not be
run at all, which can cause weird breakage.
Module::Implementation::implementation_for($package)
Given a package name, this subroutine returns the implementation that
was loaded for the package. This is not a full package name, just the
suffix that identifies the implementation. For the "SYNOPSIS" example,
this subroutine would be called as
"Module::Implementation::implementation_for('Foo::Bar')", and it would
return "XS" or "PurePerl".
HOW THE IMPLEMENTATION LOADER WORKS
The implementation loader works like this ...
First, it checks for an %ENV var specifying the implementation to load.
The env var is based on the package name which loads the
implementations. The "::" package separator is replaced with "_", and
made entirely upper-case. Finally, we append "_IMPLEMENTATION" to this
name.
So in our "SYNOPSIS" example, the corresponding %ENV key would be
"FOO_BAR_IMPLEMENTATION".
If this is set, then the loader will only try to load this one
implementation.
If the env var requests an implementation which doesn't match one of
the implementations specified when the loader was created, an error is
thrown.
If this one implementation fails to load then loader throws an error.
This is useful for testing. You can request a specific implementation
in a test file by writing something like this:
BEGIN { $ENV{FOO_BAR_IMPLEMENTATION} = 'XS' }
use Foo::Bar;
If the environment variable is not set, then the loader simply tries
the implementations originally passed to "Module::Implementation". The
implementations are tried in the order in which they were originally
passed.
The loader will use the first implementation that loads without an
error. It will copy any requested symbols from this implementation.
If none of the implementations can be loaded, then the loader throws an
exception.
The loader returns the name of the package it loaded.
AUTHOR
Dave Rolsky <autarch@urth.org>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2013 by Dave Rolsky.
This is free software, licensed under:
The Artistic License 2.0 (GPL Compatible)
perl v5.18.1 2013-07-14 Module::Implementation(3)
