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1 | package Import::Into; |
2 | |
3 | use strict; |
4 | use warnings FATAL => 'all'; |
5 | |
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6 | our $VERSION = '1.000003'; # 1.0.3 |
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7 | |
8 | my %importers; |
9 | |
10 | sub import::into { |
11 | my ($class, $target, @args) = @_; |
12 | $class->${\( |
13 | $importers{$target} ||= eval qq{ |
14 | package $target; |
15 | sub { shift->import(\@_) }; |
16 | } or die "Couldn't build importer for $target: $@" |
17 | )}(@args); |
18 | } |
19 | |
20 | 1; |
21 | |
22 | =head1 NAME |
23 | |
24 | Import::Into - import packages into other packages |
25 | |
26 | =head1 SYNOPSIS |
27 | |
28 | package My::MultiExporter; |
29 | |
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30 | use Import::Into; |
31 | |
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32 | use Thing1 (); |
33 | use Thing2 (); |
34 | |
35 | sub import { |
36 | my $target = caller; |
37 | Thing1->import::into($target); |
38 | Thing2->import::into($target, qw(import arguments)); |
39 | } |
40 | |
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41 | Note: you don't need to do anything more clever than this provided you |
42 | document that people wanting to re-export your module should also be using |
43 | L<Import::Into>. In fact, for a single module you can simply do: |
44 | |
45 | sub import { |
46 | ... |
47 | Thing1->import::into(scalar caller); |
48 | } |
49 | |
50 | Notably, this works: |
51 | |
52 | use base qw(Exporter); |
53 | |
54 | sub import { |
55 | shift->export_to_level(1); |
56 | Thing1->import::into(scalar caller); |
57 | } |
58 | |
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59 | Note 2: You do B<not> need to do anything to Thing1 to be able to call |
60 | C<import::into> on it. This is a global method, and is callable on any |
61 | package (and in fact on any object as well, although it's rarer that you'd |
62 | want to do that). |
63 | |
64 | If how and why this all works is of interest to you, please read on to the |
65 | description immediately below. |
66 | |
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67 | =head1 DESCRIPTION |
68 | |
69 | Writing exporters is a pain. Some use L<Exporter>, some use L<Sub::Exporter>, |
70 | some use L<Moose::Exporter>, some use L<Exporter::Declare> ... and some things |
71 | are pragmas. |
72 | |
73 | If you want to re-export other things, you have to know which is which. |
74 | L<Exporter> subclasses provide export_to_level, but if they overrode their |
75 | import method all bets are off. L<Sub::Exporter> provides an into parameter |
76 | but figuring out something used it isn't trivial. Pragmas need to have |
77 | their C<import> method called directly since they affect the current unit of |
78 | compilation. |
79 | |
80 | It's ... annoying. |
81 | |
82 | However, there is an approach that actually works for all of these types. |
83 | |
84 | eval "package $target; use $thing;" |
85 | |
86 | will work for anything checking caller, which is everything except pragmas. |
87 | But it doesn't work for pragmas - pragmas need: |
88 | |
89 | $thing->import; |
90 | |
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91 | because they're designed to affect the code currently being compiled - so |
92 | within an eval, that's the scope of the eval itself, not the module that |
93 | just C<use>d you - so |
94 | |
95 | sub import { |
96 | eval "use strict;" |
97 | } |
98 | |
99 | doesn't do what you wanted, but |
100 | |
101 | sub import { |
102 | strict->import; |
103 | } |
104 | |
105 | will apply L<strict> to the calling file correctly. |
106 | |
107 | Of course, now you have two new problems - first, that you still need to |
108 | know if something's a pragma, and second that you can't use either of |
109 | these approaches alone on something like L<Moose> or L<Moo> that's both |
110 | an exporter and a pragma. |
111 | |
112 | So, the complete solution is: |
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113 | |
114 | my $sub = eval "package $target; sub { shift->import(\@_) }"; |
115 | $sub->($thing, @import_args); |
116 | |
117 | which means that import is called from the right place for pragmas to take |
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118 | effect, and from the right package for caller checking to work - and so |
119 | behaves correctly for all types of exporter, for pragmas, and for hybrids. |
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120 | |
121 | Remembering all this, however, is excessively irritating. So I wrote a module |
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122 | so I didn't have to anymore. Loading L<Import::Into> creates a global method |
123 | C<import::into> which you can call on any package to import it into another |
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124 | package. So now you can simply write: |
125 | |
126 | use Import::Into; |
127 | |
128 | $thing->import::into($target, @import_args); |
129 | |
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130 | This works because of how perl resolves method calls - a call to a simple |
131 | method name is resolved against the package of the class or object, so |
132 | |
133 | $thing->method_name(@args); |
134 | |
135 | is roughly equivalent to: |
136 | |
137 | my $code_ref = $thing->can('method_name'); |
138 | $code_ref->($thing, @args); |
139 | |
140 | while if a C<::> is found, the lookup is made relative to the package name |
141 | (i.e. everything before the last C<::>) so |
142 | |
143 | $thing->Package::Name::method_name(@args); |
144 | |
145 | is roughly equivalent to: |
146 | |
147 | my $code_ref = Package::Name->can('method_name'); |
148 | $code_ref->($thing, @args); |
149 | |
150 | So since L<Import::Into> defines a method C<into> in package C<import> |
151 | the syntax reliably calls that. |
152 | |
153 | For more craziness of this order, have a look at the article I wrote at |
154 | L<http://shadow.cat/blog/matt-s-trout/madness-with-methods> which covers |
155 | coderef abuse and the C<${\...}> syntax. |
156 | |
157 | Final note: You do still need to ensure that you already loaded C<$thing> - if |
158 | you're receiving this from a parameter, I recommend using L<Module::Runtime>: |
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159 | |
160 | use Import::Into; |
161 | use Module::Runtime qw(use_module); |
162 | |
163 | use_module($thing)->import::into($target, @import_args); |
164 | |
165 | And that's it. |
166 | |
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167 | =head1 AUTHOR |
168 | |
169 | mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk> |
170 | |
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171 | =head1 CONTRIBUTORS |
172 | |
173 | None yet - maybe this software is perfect! (ahahahahahahahahaha) |
174 | |
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175 | =head1 COPYRIGHT |
176 | |
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177 | Copyright (c) 2012 the Import::Into L</AUTHOR> and L</CONTRIBUTORS> |
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178 | as listed above. |
179 | |
180 | =head1 LICENSE |
181 | |
182 | This library is free software and may be distributed under the same terms |
183 | as perl itself. |