1Module::Implementation(U3s)er Contributed Perl DocumentatMioodnule::Implementation(3)
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NAME

6       Module::Implementation - Loads one of several alternate underlying
7       implementations for a module
8

VERSION

10       version 0.09
11

SYNOPSIS

13         package Foo::Bar;
14
15         use Module::Implementation;
16
17         BEGIN {
18             my $loader = Module::Implementation::build_loader_sub(
19                 implementations => [ 'XS',  'PurePerl' ],
20                 symbols         => [ 'run', 'check' ],
21             );
22
23             $loader->();
24         }
25
26         package Consumer;
27
28         # loads the first viable implementation
29         use Foo::Bar;
30

DESCRIPTION

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.
37
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.
41

API

43       This module provides two subroutines, neither of which are exported.
44
45   Module::Implementation::build_loader_sub(...)
46       This subroutine takes the following arguments.
47
48       ·   implementations
49
50           This should be an array reference of implementation names. Each
51           name should correspond to a module in the caller's namespace.
52
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
56           This argument is required.
57
58       ·   symbols
59
60           A list of symbols to copy from the implementation package to the
61           calling package.
62
63           These can be prefixed with a variable type: "$", "@", "%", "&", or
64           "*)". If no prefix is given, the symbol is assumed to be a
65           subroutine.
66
67           This argument is optional.
68
69       This subroutine returns the implementation loader as a sub reference.
70
71       It is up to you to call this loader sub in your code.
72
73       I recommend that you do not call this loader in an "import()" sub. If a
74       caller explicitly requests no imports, your "import()" sub will not be
75       run at all, which can cause weird breakage.
76
77   Module::Implementation::implementation_for($package)
78       Given a package name, this subroutine returns the implementation that
79       was loaded for the package. This is not a full package name, just the
80       suffix that identifies the implementation. For the "SYNOPSIS" example,
81       this subroutine would be called as
82       "Module::Implementation::implementation_for('Foo::Bar')", and it would
83       return "XS" or "PurePerl".
84

HOW THE IMPLEMENTATION LOADER WORKS

86       The implementation loader works like this ...
87
88       First, it checks for an %ENV var specifying the implementation to load.
89       The env var is based on the package name which loads the
90       implementations. The "::" package separator is replaced with "_", and
91       made entirely upper-case. Finally, we append "_IMPLEMENTATION" to this
92       name.
93
94       So in our "SYNOPSIS" example, the corresponding %ENV key would be
95       "FOO_BAR_IMPLEMENTATION".
96
97       If this is set, then the loader will only try to load this one
98       implementation.
99
100       If the env var requests an implementation which doesn't match one of
101       the implementations specified when the loader was created, an error is
102       thrown.
103
104       If this one implementation fails to load then loader throws an error.
105       This is useful for testing. You can request a specific implementation
106       in a test file by writing something like this:
107
108         BEGIN { $ENV{FOO_BAR_IMPLEMENTATION} = 'XS' }
109         use Foo::Bar;
110
111       If the environment variable is not set, then the loader simply tries
112       the implementations originally passed to "Module::Implementation". The
113       implementations are tried in the order in which they were originally
114       passed.
115
116       The loader will use the first implementation that loads without an
117       error. It will copy any requested symbols from this implementation.
118
119       If none of the implementations can be loaded, then the loader throws an
120       exception.
121
122       The loader returns the name of the package it loaded.
123

AUTHOR

125       Dave Rolsky <autarch@urth.org>
126

128       This software is Copyright (c) 2014 by Dave Rolsky.
129
130       This is free software, licensed under:
131
132         The Artistic License 2.0 (GPL Compatible)
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136perl v5.30.0                      2019-07-26         Module::Implementation(3)
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