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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 = '1.001000'; # 1.1.0 |
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7 | |
8 | my %importers; |
9 | |
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10 | sub _importer { |
11 | my $target = shift; |
12 | \($importers{$target} ||= eval qq{ |
13 | package $target; |
14 | sub { my \$m = splice \@_, 1, 1; shift->\$m(\@_) }; |
15 | } or die "Couldn't build importer for $target: $@") |
16 | } |
17 | |
18 | |
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19 | sub import::into { |
20 | my ($class, $target, @args) = @_; |
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21 | $class->${_importer($target)}(import => @args); |
22 | } |
23 | |
24 | sub unimport::out_of { |
25 | my ($class, $target, @args) = @_; |
26 | $class->${_importer($target)}(unimport => @args); |
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27 | } |
28 | |
29 | 1; |
30 | |
31 | =head1 NAME |
32 | |
33 | Import::Into - import packages into other packages |
34 | |
35 | =head1 SYNOPSIS |
36 | |
37 | package My::MultiExporter; |
38 | |
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39 | use Import::Into; |
40 | |
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41 | use Thing1 (); |
42 | use Thing2 (); |
43 | |
44 | sub import { |
45 | my $target = caller; |
46 | Thing1->import::into($target); |
47 | Thing2->import::into($target, qw(import arguments)); |
48 | } |
49 | |
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50 | Note: you don't need to do anything more clever than this provided you |
51 | document that people wanting to re-export your module should also be using |
52 | L<Import::Into>. In fact, for a single module you can simply do: |
53 | |
54 | sub import { |
55 | ... |
56 | Thing1->import::into(scalar caller); |
57 | } |
58 | |
59 | Notably, this works: |
60 | |
61 | use base qw(Exporter); |
62 | |
63 | sub import { |
64 | shift->export_to_level(1); |
65 | Thing1->import::into(scalar caller); |
66 | } |
67 | |
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68 | Note 2: You do B<not> need to do anything to Thing1 to be able to call |
69 | C<import::into> on it. This is a global method, and is callable on any |
70 | package (and in fact on any object as well, although it's rarer that you'd |
71 | want to do that). |
72 | |
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73 | Finally, we also provide an C<unimport::out_of> to allow the exporting of the |
74 | effect of C<no>: |
75 | |
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76 | # unimport::out_of was added in 1.1.0 (1.001000) |
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77 | sub unimport { |
78 | Moose->unimport::out_of(scalar caller); # no MyThing == no Moose |
79 | } |
80 | |
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81 | If how and why this all works is of interest to you, please read on to the |
82 | description immediately below. |
83 | |
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84 | =head1 DESCRIPTION |
85 | |
86 | Writing exporters is a pain. Some use L<Exporter>, some use L<Sub::Exporter>, |
87 | some use L<Moose::Exporter>, some use L<Exporter::Declare> ... and some things |
88 | are pragmas. |
89 | |
90 | If you want to re-export other things, you have to know which is which. |
91 | L<Exporter> subclasses provide export_to_level, but if they overrode their |
92 | import method all bets are off. L<Sub::Exporter> provides an into parameter |
93 | but figuring out something used it isn't trivial. Pragmas need to have |
94 | their C<import> method called directly since they affect the current unit of |
95 | compilation. |
96 | |
97 | It's ... annoying. |
98 | |
99 | However, there is an approach that actually works for all of these types. |
100 | |
101 | eval "package $target; use $thing;" |
102 | |
103 | will work for anything checking caller, which is everything except pragmas. |
104 | But it doesn't work for pragmas - pragmas need: |
105 | |
106 | $thing->import; |
107 | |
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108 | because they're designed to affect the code currently being compiled - so |
109 | within an eval, that's the scope of the eval itself, not the module that |
110 | just C<use>d you - so |
111 | |
112 | sub import { |
113 | eval "use strict;" |
114 | } |
115 | |
116 | doesn't do what you wanted, but |
117 | |
118 | sub import { |
119 | strict->import; |
120 | } |
121 | |
122 | will apply L<strict> to the calling file correctly. |
123 | |
124 | Of course, now you have two new problems - first, that you still need to |
125 | know if something's a pragma, and second that you can't use either of |
126 | these approaches alone on something like L<Moose> or L<Moo> that's both |
127 | an exporter and a pragma. |
128 | |
129 | So, the complete solution is: |
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130 | |
131 | my $sub = eval "package $target; sub { shift->import(\@_) }"; |
132 | $sub->($thing, @import_args); |
133 | |
134 | which means that import is called from the right place for pragmas to take |
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135 | effect, and from the right package for caller checking to work - and so |
136 | behaves correctly for all types of exporter, for pragmas, and for hybrids. |
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137 | |
138 | Remembering all this, however, is excessively irritating. So I wrote a module |
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139 | so I didn't have to anymore. Loading L<Import::Into> creates a global method |
140 | C<import::into> which you can call on any package to import it into another |
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141 | package. So now you can simply write: |
142 | |
143 | use Import::Into; |
144 | |
145 | $thing->import::into($target, @import_args); |
146 | |
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147 | This works because of how perl resolves method calls - a call to a simple |
148 | method name is resolved against the package of the class or object, so |
149 | |
150 | $thing->method_name(@args); |
151 | |
152 | is roughly equivalent to: |
153 | |
154 | my $code_ref = $thing->can('method_name'); |
155 | $code_ref->($thing, @args); |
156 | |
157 | while if a C<::> is found, the lookup is made relative to the package name |
158 | (i.e. everything before the last C<::>) so |
159 | |
160 | $thing->Package::Name::method_name(@args); |
161 | |
162 | is roughly equivalent to: |
163 | |
164 | my $code_ref = Package::Name->can('method_name'); |
165 | $code_ref->($thing, @args); |
166 | |
167 | So since L<Import::Into> defines a method C<into> in package C<import> |
168 | the syntax reliably calls that. |
169 | |
170 | For more craziness of this order, have a look at the article I wrote at |
171 | L<http://shadow.cat/blog/matt-s-trout/madness-with-methods> which covers |
172 | coderef abuse and the C<${\...}> syntax. |
173 | |
174 | Final note: You do still need to ensure that you already loaded C<$thing> - if |
175 | you're receiving this from a parameter, I recommend using L<Module::Runtime>: |
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176 | |
177 | use Import::Into; |
178 | use Module::Runtime qw(use_module); |
179 | |
180 | use_module($thing)->import::into($target, @import_args); |
181 | |
182 | And that's it. |
183 | |
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184 | =head1 AUTHOR |
185 | |
186 | mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk> |
187 | |
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188 | =head1 CONTRIBUTORS |
189 | |
190 | None yet - maybe this software is perfect! (ahahahahahahahahaha) |
191 | |
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192 | =head1 COPYRIGHT |
193 | |
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194 | Copyright (c) 2012 the Import::Into L</AUTHOR> and L</CONTRIBUTORS> |
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195 | as listed above. |
196 | |
197 | =head1 LICENSE |
198 | |
199 | This library is free software and may be distributed under the same terms |
200 | as perl itself. |