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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 = '1.001001'; # 1.1.1 |
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7 | |
8 | my %importers; |
9 | |
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10 | sub _importer { |
11 | my $target = shift; |
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12 | my ($package, $file, $line) |
13 | = $target =~ /[^0-9]/ ? ($target) : caller($target + 1); |
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14 | my $code = qq{package $package;\n} |
15 | . ($file ? "#line $line \"$file\"\n" : '') |
16 | . 'sub { my $m = splice @_, 1, 1; shift->$m(@_) };'."\n"; |
17 | my $sub = \(eval $code |
18 | or die "Couldn't build importer for $package: $@"); |
19 | $importers{$target} = $sub |
20 | unless $file; |
21 | $sub; |
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22 | } |
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23 | |
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24 | sub import::into { |
25 | my ($class, $target, @args) = @_; |
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26 | $class->${_importer($target)}(import => @args); |
27 | } |
28 | |
29 | sub unimport::out_of { |
30 | my ($class, $target, @args) = @_; |
31 | $class->${_importer($target)}(unimport => @args); |
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32 | } |
33 | |
34 | 1; |
35 | |
36 | =head1 NAME |
37 | |
38 | Import::Into - import packages into other packages |
39 | |
40 | =head1 SYNOPSIS |
41 | |
42 | package My::MultiExporter; |
43 | |
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44 | use Import::Into; |
45 | |
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46 | use Thing1 (); |
47 | use Thing2 (); |
48 | |
49 | sub import { |
50 | my $target = caller; |
51 | Thing1->import::into($target); |
52 | Thing2->import::into($target, qw(import arguments)); |
53 | } |
54 | |
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55 | Note: you don't need to do anything more clever than this provided you |
56 | document that people wanting to re-export your module should also be using |
57 | L<Import::Into>. In fact, for a single module you can simply do: |
58 | |
59 | sub import { |
60 | ... |
61 | Thing1->import::into(scalar caller); |
62 | } |
63 | |
64 | Notably, this works: |
65 | |
66 | use base qw(Exporter); |
67 | |
68 | sub import { |
69 | shift->export_to_level(1); |
70 | Thing1->import::into(scalar caller); |
71 | } |
72 | |
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73 | Note 2: You do B<not> need to do anything to Thing1 to be able to call |
74 | C<import::into> on it. This is a global method, and is callable on any |
75 | package (and in fact on any object as well, although it's rarer that you'd |
76 | want to do that). |
77 | |
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78 | Finally, we also provide an C<unimport::out_of> to allow the exporting of the |
79 | effect of C<no>: |
80 | |
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81 | # unimport::out_of was added in 1.1.0 (1.001000) |
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82 | sub unimport { |
83 | Moose->unimport::out_of(scalar caller); # no MyThing == no Moose |
84 | } |
85 | |
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86 | If how and why this all works is of interest to you, please read on to the |
87 | description immediately below. |
88 | |
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89 | =head1 DESCRIPTION |
90 | |
91 | Writing exporters is a pain. Some use L<Exporter>, some use L<Sub::Exporter>, |
92 | some use L<Moose::Exporter>, some use L<Exporter::Declare> ... and some things |
93 | are pragmas. |
94 | |
95 | If you want to re-export other things, you have to know which is which. |
96 | L<Exporter> subclasses provide export_to_level, but if they overrode their |
97 | import method all bets are off. L<Sub::Exporter> provides an into parameter |
98 | but figuring out something used it isn't trivial. Pragmas need to have |
99 | their C<import> method called directly since they affect the current unit of |
100 | compilation. |
101 | |
102 | It's ... annoying. |
103 | |
104 | However, there is an approach that actually works for all of these types. |
105 | |
106 | eval "package $target; use $thing;" |
107 | |
108 | will work for anything checking caller, which is everything except pragmas. |
109 | But it doesn't work for pragmas - pragmas need: |
110 | |
111 | $thing->import; |
112 | |
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113 | because they're designed to affect the code currently being compiled - so |
114 | within an eval, that's the scope of the eval itself, not the module that |
115 | just C<use>d you - so |
116 | |
117 | sub import { |
118 | eval "use strict;" |
119 | } |
120 | |
121 | doesn't do what you wanted, but |
122 | |
123 | sub import { |
124 | strict->import; |
125 | } |
126 | |
127 | will apply L<strict> to the calling file correctly. |
128 | |
129 | Of course, now you have two new problems - first, that you still need to |
130 | know if something's a pragma, and second that you can't use either of |
131 | these approaches alone on something like L<Moose> or L<Moo> that's both |
132 | an exporter and a pragma. |
133 | |
134 | So, the complete solution is: |
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135 | |
136 | my $sub = eval "package $target; sub { shift->import(\@_) }"; |
137 | $sub->($thing, @import_args); |
138 | |
139 | which means that import is called from the right place for pragmas to take |
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140 | effect, and from the right package for caller checking to work - and so |
141 | behaves correctly for all types of exporter, for pragmas, and for hybrids. |
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142 | |
143 | Remembering all this, however, is excessively irritating. So I wrote a module |
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144 | so I didn't have to anymore. Loading L<Import::Into> creates a global method |
145 | C<import::into> which you can call on any package to import it into another |
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146 | package. So now you can simply write: |
147 | |
148 | use Import::Into; |
149 | |
150 | $thing->import::into($target, @import_args); |
151 | |
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152 | This works because of how perl resolves method calls - a call to a simple |
153 | method name is resolved against the package of the class or object, so |
154 | |
155 | $thing->method_name(@args); |
156 | |
157 | is roughly equivalent to: |
158 | |
159 | my $code_ref = $thing->can('method_name'); |
160 | $code_ref->($thing, @args); |
161 | |
162 | while if a C<::> is found, the lookup is made relative to the package name |
163 | (i.e. everything before the last C<::>) so |
164 | |
165 | $thing->Package::Name::method_name(@args); |
166 | |
167 | is roughly equivalent to: |
168 | |
169 | my $code_ref = Package::Name->can('method_name'); |
170 | $code_ref->($thing, @args); |
171 | |
172 | So since L<Import::Into> defines a method C<into> in package C<import> |
173 | the syntax reliably calls that. |
174 | |
175 | For more craziness of this order, have a look at the article I wrote at |
176 | L<http://shadow.cat/blog/matt-s-trout/madness-with-methods> which covers |
177 | coderef abuse and the C<${\...}> syntax. |
178 | |
179 | Final note: You do still need to ensure that you already loaded C<$thing> - if |
180 | you're receiving this from a parameter, I recommend using L<Module::Runtime>: |
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181 | |
182 | use Import::Into; |
183 | use Module::Runtime qw(use_module); |
184 | |
185 | use_module($thing)->import::into($target, @import_args); |
186 | |
187 | And that's it. |
188 | |
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189 | =head1 ACKNOWLEDGEMENTS |
190 | |
191 | Thanks to Getty for asking "how can I get C<< use strict; use warnings; >> |
192 | turned on for all consumers of my code?" and then "why is this not a |
193 | module?!". |
194 | |
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195 | =head1 AUTHOR |
196 | |
197 | mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk> |
198 | |
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199 | =head1 CONTRIBUTORS |
200 | |
201 | None yet - maybe this software is perfect! (ahahahahahahahahaha) |
202 | |
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203 | =head1 COPYRIGHT |
204 | |
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205 | Copyright (c) 2012 the Import::Into L</AUTHOR> and L</CONTRIBUTORS> |
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206 | as listed above. |
207 | |
208 | =head1 LICENSE |
209 | |
210 | This library is free software and may be distributed under the same terms |
211 | as perl itself. |