1Module::Implementation(U3s)er Contributed Perl DocumentatMioodnule::Implementation(3)
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6 Module::Implementation - Loads one of several alternate underlying
7 implementations for a module
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10 version 0.06
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13 package Foo::Bar;
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15 use Module::Implementation;
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17 BEGIN {
18 my $loader = Module::Implementation::build_loader_sub(
19 implementations => [ 'XS', 'PurePerl' ],
20 symbols => [ 'run', 'check' ],
21 );
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23 $loader->();
24 }
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26 package Consumer;
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28 # loads the first viable implementation
29 use Foo::Bar;
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32 This module abstracts out the process of choosing one of several
33 underlying implementations for a module. This can be used to provide XS
34 and pure Perl implementations of a module, or it could be used to load
35 an implementation for a given OS or any other case of needing to
36 provide multiple implementations.
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38 This module is only useful when you know all the implementations ahead
39 of time. If you want to load arbitrary implementations then you
40 probably want something like a plugin system, not this module.
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43 This module provides two subroutines, neither of which are exported.
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45 Module::Implementation::<build_loader_sub(...)
46 This subroutine takes the following arguments.
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48 · implementations
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50 This should be an array reference of implementation names. Each
51 name should correspond to a module in the caller's namespace.
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53 In other words, using the example in the "SYNOPSIS", this module
54 will look for the "Foo::Bar::XS" and "Foo::Bar::PurePerl" modules
55 will be installed
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57 This argument is required.
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59 · symbols
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61 A list of symbols to copy from the implementation package to the
62 calling package.
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64 These can be prefixed with a variable type: "$", "@", "%", "&", or
65 "*)". If no prefix is given, the symbol is assumed to be a
66 subroutine.
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68 This argument is optional.
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70 This subroutine returns the implementation loader as a sub reference.
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72 It is up to you to call this loader sub in your code.
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74 I recommend that you do not call this loader in an "import()" sub. If a
75 caller explicitly requests no imports, your "import()" sub will not be
76 run at all, which can cause weird breakage.
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78 Module::Implementation::implementation_for($package)
79 Given a package name, this subroutine returns the implementation that
80 was loaded for the package. This is not a full package name, just the
81 suffix that identifies the implementation. For the "SYNOPSIS" example,
82 this subroutine would be called as
83 "Module::Implementation::implementation_for('Foo::Bar')", and it would
84 return "XS" or "PurePerl".
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87 The implementation loader works like this ...
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89 First, it checks for an %ENV var specifying the implementation to load.
90 The env var is based on the package name which loads the
91 implementations. The "::" package separator is replaced with "_", and
92 made entirely upper-case. Finally, we append "_IMPLEMENTATION" to this
93 name.
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95 So in our "SYNOPSIS" example, the corresponding %ENV key would be
96 "FOO_BAR_IMPLEMENTATION".
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98 If this is set, then the loader will only try to load this one
99 implementation.
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101 If the env var requests an implementation which doesn't match one of
102 the implementations specified when the loader was created, an error is
103 thrown.
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105 If this one implementation fails to load then loader throws an error.
106 This is useful for testing. You can request a specific implementation
107 in a test file by writing something like this:
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109 BEGIN { $ENV{FOO_BAR_IMPLEMENTATION} = 'XS' }
110 use Foo::Bar;
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112 If the environment variable is not set, then the loader simply tries
113 the implementations originally passed to "Module::Implementation". The
114 implementations are tried in the order in which they were originally
115 passed.
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117 The loader will use the first implementation that loads without an
118 error. It will copy any requested symbols from this implementation.
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120 If none of the implementations can be loaded, then the loader throws an
121 exception.
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123 The loader returns the name of the package it loaded.
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126 Dave Rolsky <autarch@urth.org>
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129 This software is Copyright (c) 2012 by Dave Rolsky.
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131 This is free software, licensed under:
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133 The Artistic License 2.0 (GPL Compatible)
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137perl v5.16.3 2012-02-12 Module::Implementation(3)