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1 | package Package::Variant; |
2 | |
3 | use strictures 1; |
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4 | use Carp qw( croak ); |
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5 | |
6 | our %Variable; |
7 | |
8 | sub import { |
9 | my $target = caller; |
10 | my $me = shift; |
11 | my $last = (split '::', $target)[-1]; |
12 | my $anon = 'A000'; |
13 | my $variable = $target; |
14 | my %args = @_; |
15 | no strict 'refs'; |
16 | $Variable{$variable} = { |
17 | anon => $anon, |
18 | args => \%args, |
19 | subs => { |
20 | map +($_ => sub {}), @{$args{subs}||[]}, |
21 | }, |
22 | }; |
23 | *{"${target}::import"} = sub { |
24 | my $target = caller; |
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25 | my (undef, %arg) = @_; |
26 | my $as = defined($arg{as}) ? $arg{as} : $last; |
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27 | no strict 'refs'; |
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28 | *{"${target}::${as}"} = sub { |
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29 | $me->build_variant_of($variable, @_); |
30 | }; |
31 | }; |
32 | my $subs = $Variable{$variable}{subs}; |
33 | foreach my $name (keys %$subs) { |
34 | *{"${target}::${name}"} = sub { |
35 | goto &{$subs->{$name}} |
36 | }; |
37 | } |
38 | *{"${target}::install"} = sub { |
39 | goto &{$Variable{$variable}{install}}; |
40 | } |
41 | } |
42 | |
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43 | my $sanitize_importing = sub { |
44 | my ($me, $spec) = @_; |
45 | return [] |
46 | unless defined $spec; |
47 | return [map [$_ => $spec->{$_}], keys %$spec] |
48 | if ref $spec eq 'HASH'; |
49 | croak q{The 'importing' option has to be either a hash or array ref} |
50 | unless ref $spec eq 'ARRAY'; |
51 | my @specced = @$spec; |
52 | my @imports; |
53 | while (@specced) { |
54 | push @imports, [shift(@specced), shift(@specced)]; |
55 | } |
56 | return \@imports; |
57 | }; |
58 | |
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59 | sub build_variant_of { |
60 | my ($me, $variable, @args) = @_; |
61 | my $variant_name = "${variable}::_Variant_".++$Variable{$variable}{anon}; |
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62 | my $import = $me |
63 | ->$sanitize_importing($Variable{$variable}{args}{importing}); |
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64 | my $setup = join("\n", |
65 | "package ${variant_name};", |
66 | (map sprintf( |
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67 | q!use %s %s;!, |
68 | $import->[$_][0], |
69 | not(defined $import->[$_][1]) |
70 | ? '' |
71 | : sprintf( |
72 | q!@{$import->[%d][1]}!, |
73 | $_, |
74 | ), |
75 | ), 0..$#$import), |
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76 | "1;", |
77 | ); |
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78 | eval $setup |
79 | or die "evaling ${setup} failed: $@"; |
80 | my $subs = $Variable{$variable}{subs}; |
81 | local @{$subs}{keys %$subs} = map $variant_name->can($_), keys %$subs; |
82 | local $Variable{$variable}{install} = sub { |
83 | my ($name, $ref) = @_; |
84 | no strict 'refs'; |
85 | *{"${variant_name}::${name}"} = $ref; |
86 | }; |
87 | $variable->make_variant($variant_name, @args); |
88 | return $variant_name; |
89 | } |
90 | |
91 | 1; |
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92 | |
93 | __END__ |
94 | |
95 | =head1 NAME |
96 | |
97 | Package::Variant - Parameterizable packages |
98 | |
99 | =head1 SYNOPSIS |
100 | |
101 | # declaring a variable Moo role |
102 | package My::Role::ObjectAttr; |
103 | use strictures 1; |
104 | use Package::Variant |
105 | # what modules to 'use' |
106 | importing => { 'Moo::Role' => [] }, |
107 | # proxied subroutines |
108 | subs => [qw( has around before after extends )], |
109 | |
110 | sub make_variant { |
111 | my ($class, $target_package, %arguments) = @_; |
112 | # access arguments |
113 | my $name = $arguments{name}; |
114 | # use proxied 'has' to add an attribute |
115 | has $name => (is => 'lazy'); |
116 | # install a builder method |
117 | install "_build_${name}" => sub { |
118 | return $arguments{class}->new; |
119 | }; |
120 | } |
121 | |
122 | # using the role |
123 | package My::Class::WithObjectAttr; |
124 | use strictures 1; |
125 | use Moo; |
126 | use My::Role::ObjectAttr; |
127 | |
128 | with ObjectAttr(name => 'some_obj', class => 'Some::Class'); |
129 | |
130 | # using our class |
131 | my $obj = My::Class::WithObjectAttr->new; |
132 | $obj->some_obj; # returns a Some::Class instance |
133 | |
134 | =head1 DESCRIPTION |
135 | |
136 | This module allows you to build packages that return different variations |
137 | depending on what parameters are given. |
138 | |
139 | Users of your package will receive a subroutine able to take parameters |
140 | and return the name of a suitable variant package. The implmenetation does |
141 | not care about what kind of package it builds. |
142 | |
143 | =head2 Declaring a variable package |
144 | |
145 | There are two important parts to creating a variable package. You first |
146 | have to give C<Package::Variant> some basic information about what kind of |
147 | package you want to provide, and how. The second part is implementing a |
148 | method receiving the user's arguments and generating your variants. |
149 | |
150 | =head3 Setting up the environment for building variations |
151 | |
152 | When you C<use Package::Variant>, you pass along some arguments that |
153 | describe how you intend to build your variations. |
154 | |
155 | use Package::Variant |
156 | importing => { $package => \@import_arguments, ... }, |
157 | subs => [ @proxied_subroutine_names ]; |
158 | |
159 | The L</importing> option needs to be a hash reference with package names |
160 | to be C<use>d as keys, and array references containing the import |
161 | arguments as values. These packages will be imported into every new |
162 | variant, and need to set up every declarative subroutine you require to |
163 | build your variable package. The next option will allow you to use these |
164 | functions. |
165 | |
166 | The L</subs> option is an array reference of subroutine names that are |
167 | exported by the packages specified with L</importing>. These subroutines |
168 | will be proxied from your declaration package to the variant to be |
169 | generated. |
170 | |
171 | With L</importing> initializing your package and L</subs> declaring what |
172 | subroutines you want to use to build a variant, you can now write a |
173 | L</make_variant> method building your variants. |
174 | |
175 | =head3 Declaring a method to produce variants |
176 | |
177 | Every time a user requests a new variant a method named L</make_variant> |
178 | will be called with the name of the target package and the arguments from |
179 | the user. |
180 | |
181 | It can then use the proxied subroutines declared with L</subs> to |
182 | customize the new package. An L</install> subroutine is exported as well |
183 | allowing you to dynamically install methods into the new package. If these |
184 | options aren't flexible enough, you can use the passed name of the new |
185 | package to do any other kind of customizations. |
186 | |
187 | sub make_variant { |
188 | my ($class, $target, @arguments) = @_; |
189 | # ... |
190 | # customization goes here |
191 | # ... |
192 | } |
193 | |
194 | When the method is finished, the user will receive the name of the new |
195 | package variant you just set up. |
196 | |
197 | =head2 Using variable packages |
198 | |
199 | After your variable package is L<created|/Declaring a variable package> |
200 | your users can get a variant generating subroutine by simply importing |
201 | your package. |
202 | |
203 | use My::Variant; |
204 | my $new_variant_package = Variant( @variant_arguments ); |
205 | |
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206 | The package is now fully initialized and used. You can import the |
207 | subroutine under a different name by specifying an C<as> argument. |
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208 | |
209 | =head2 Dynamic creation of variant packages |
210 | |
211 | For regular uses, the L<normal import|/Using variable packages> provides |
212 | more than enough flexibility. However, if you want to create variations of |
213 | dynamically determined packages, you can use the L</build_variation_of> |
214 | method. |
215 | |
216 | You can use this to create variations of other packages and pass arguments |
217 | on to them to allow more modular and extensible variations. |
218 | |
219 | =head1 OPTIONS |
220 | |
221 | These are the options that can be passed when importing |
222 | C<Package::Variant>. They describe the environment in which the variants |
223 | are created. |
224 | |
225 | use Package::Variant |
226 | importing => { $package => \@import_arguments, ... }, |
227 | subs => [ @proxied_subroutines ]; |
228 | |
229 | =head2 importing |
230 | |
231 | This option is a hash reference mapping package names to array references |
232 | containing import arguments. The packages will be C<use>d with the given |
233 | arguments by every variation before the L</make_variant> method is asked |
234 | to create the package. |
235 | |
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236 | If import order is important to you, you can also pass the C<importing> |
237 | arguments as a flag array reference: |
238 | |
239 | use Package::Variant |
240 | importing => [ PackageA => [], PackageB => [] ]; |
241 | |
242 | If you want to import whatever the package exports by default, you have to |
243 | pass C<undef> instead of an empty array reference. |
244 | |
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245 | =head2 subs |
246 | |
247 | An array reference of strings listing the names of subroutines that should |
248 | be proxied. These subroutines are expected to be installed into the new |
249 | variant package by the modules imported with L</importing>. Subroutines |
250 | with the same name will be availabe in your declaration package, and will |
251 | proxy through to the newly created package when used within |
252 | L</make_variant>. |
253 | |
254 | =head1 VARIABLE PACKAGE METHODS |
255 | |
256 | These are methods on the variable package you declare when you import |
257 | C<Package::Variant>. |
258 | |
259 | =head2 make_variant |
260 | |
261 | Some::Variant::Package->make_variant( $target, @arguments ); |
262 | |
263 | B<You need to provide this method.> This method will be called for every |
264 | new variant of your package. This method should use the subroutines |
265 | declared in L</subs> to customize the new variant package. |
266 | |
267 | This is a class method receiving the C<$target> package and the |
268 | C<@arguments> defining the requested variant. |
269 | |
270 | =head2 import |
271 | |
272 | use Some::Variant::Package; |
273 | my $variant_package = Package( @arguments ); |
274 | |
275 | This method is provided for you. It will allow a user to C<use> your |
276 | package and receive a subroutine taking C<@arguments> defining the variant |
277 | and returning the name of the newly created variant package. |
278 | |
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279 | The following options can be specified when importing: |
280 | |
281 | =over |
282 | |
283 | =item * B<as> |
284 | |
285 | use Some::Variant::Package as => 'Foo'; |
286 | my $variant_package = Foo( @arguments ); |
287 | |
288 | Exports the generator subroutine under a different name than the default. |
289 | |
290 | =back |
291 | |
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292 | =head1 C<Package::Variant> METHODS |
293 | |
294 | These methods are available on C<Package::Variant> itself. |
295 | |
296 | =head2 build_variation_of |
297 | |
298 | my $variant_package = Package::Variant |
299 | ->build_variation_of( $variable_package, @arguments ); |
300 | |
301 | This is the dynamic method of creating new variants. It takes the |
302 | C<$variable_package>, which is a pre-declared variable package, and a set |
303 | of C<@arguments> passed to the package to generate a new |
304 | C<$variant_package>, which will be returned. |
305 | |
306 | =head2 import |
307 | |
308 | use Package::Variant @options; |
309 | |
310 | Sets up the environment in which you declare the variants of your |
311 | packages. See L</OPTIONS> for details on the available options and |
312 | L</EXPORTS> for a list of exported subroutines. |
313 | |
314 | =head1 EXPORTS |
315 | |
316 | Additionally to the proxies for subroutines provided in L</subs>, the |
317 | following exports will be available in your variable package: |
318 | |
319 | =head2 install |
320 | |
321 | install( $method_name, $code_reference ); |
322 | |
323 | Installs a method with the given C<$method_name> into the newly created |
324 | variant package. The C<$code_reference> will be used as the body for the |
325 | method. |
326 | |
327 | =head1 AUTHOR |
328 | |
329 | =over |
330 | |
331 | =item mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk> |
332 | |
333 | =back |
334 | |
335 | =head1 COPYRIGHT |
336 | |
337 | Copyright (c) 2010-2011 the C<Package::Stash> L</AUTHOR> as listed above. |
338 | |
339 | =head1 LICENSE |
340 | |
341 | This library is free software and may be distributed under the same |
342 | terms as perl itself. |
343 | |
344 | =cut |