1Sub::Exporter::TutorialU(s3e)r Contributed Perl DocumentaStuibo:n:Exporter::Tutorial(3)
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NAME

6       Sub::Exporter::Tutorial - a friendly guide to exporting with
7       Sub::Exporter
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VERSION

10       version 0.987
11

DESCRIPTION

13   What's an Exporter?
14       When you "use" a module, first it is required, then its "import" method
15       is called.  The Perl documentation tells us that the following two
16       lines are equivalent:
17
18         use Module LIST;
19
20         BEGIN { require Module; Module->import(LIST); }
21
22       The method named "import" is the module's exporter, it exports
23       functions and variables into its caller's namespace.
24
25   The Basics of Sub::Exporter
26       Sub::Exporter builds a custom exporter which can then be installed into
27       your module.  It builds this method based on configuration passed to
28       its "setup_exporter" method.
29
30       A very basic use case might look like this:
31
32         package Addition;
33         use Sub::Exporter;
34         Sub::Exporter::setup_exporter({ exports => [ qw(plus) ]});
35
36         sub plus { my ($x, $y) = @_; return $x + $y; }
37
38       This would mean that when someone used your Addition module, they could
39       have its "plus" routine imported into their package:
40
41         use Addition qw(plus);
42
43         my $z = plus(2, 2); # this works, because now plus is in the main package
44
45       That syntax to set up the exporter, above, is a little verbose, so for
46       the simple case of just naming some exports, you can write this:
47
48         use Sub::Exporter -setup => { exports => [ qw(plus) ] };
49
50       ...which is the same as the original example -- except that now the
51       exporter is built and installed at compile time.  Well, that and you
52       typed less.
53
54   Using Export Groups
55       You can specify whole groups of things that should be exportable
56       together.  These are called groups.  Exporter calls these tags.  To
57       specify groups, you just pass a "groups" key in your exporter
58       configuration:
59
60         package Food;
61         use Sub::Exporter -setup => {
62           exports => [ qw(apple banana beef fluff lox rabbit) ],
63           groups  => {
64             fauna  => [ qw(beef lox rabbit) ],
65             flora  => [ qw(apple banana) ],
66           }
67         };
68
69       Now, to import all that delicious foreign meat, your consumer needs
70       only to write:
71
72         use Food qw(:fauna);
73         use Food qw(-fauna);
74
75       Either one of the above is acceptable.  A colon is more traditional,
76       but barewords with a leading colon can't be enquoted by a fat arrow.
77       We'll see why that matters later on.
78
79       Groups can contain other groups.  If you include a group name (with the
80       leading dash or colon) in a group definition, it will be expanded
81       recursively when the exporter is called.  The exporter will not recurse
82       into the same group twice while expanding groups.
83
84       There are two special groups:  "all" and "default".  The "all" group is
85       defined for you and contains all exportable subs.  You can redefine it,
86       if you want to export only a subset when all exports are requested.
87       The "default" group is the set of routines to export when nothing
88       specific is requested.  By default, there is no "default" group.
89
90   Renaming Your Imports
91       Sometimes you want to import something, but you don't like the name as
92       which it's imported.  Sub::Exporter can rename your imports for you.
93       If you wanted to import "lox" from the Food package, but you don't like
94       the name, you could write this:
95
96         use Food lox => { -as => 'salmon' };
97
98       Now you'd get the "lox" routine, but it would be called salmon in your
99       package.  You can also rename entire groups by using the "prefix"
100       option:
101
102         use Food -fauna => { -prefix => 'cute_little_' };
103
104       Now you can call your "cute_little_rabbit" routine.  (You can also call
105       "cute_little_beef", but that hardly seems as enticing.)
106
107       When you define groups, you can include renaming.
108
109         use Sub::Exporter -setup => {
110           exports => [ qw(apple banana beef fluff lox rabbit) ],
111           groups  => {
112             fauna  => [ qw(beef lox), rabbit => { -as => 'coney' } ],
113           }
114         };
115
116       A prefix on a group like that does the right thing.  This is when it's
117       useful to use a dash instead of a colon to indicate a group: you can
118       put a fat arrow between the group and its arguments, then.
119
120         use Food -fauna => { -prefix => 'lovely_' };
121
122         eat( lovely_coney ); # this works
123
124       Prefixes also apply recursively.  That means that this code works:
125
126         use Sub::Exporter -setup => {
127           exports => [ qw(apple banana beef fluff lox rabbit) ],
128           groups  => {
129             fauna   => [ qw(beef lox), rabbit => { -as => 'coney' } ],
130             allowed => [ -fauna => { -prefix => 'willing_' }, 'banana' ],
131           }
132         };
133
134         ...
135
136         use Food -allowed => { -prefix => 'any_' };
137
138         $dinner = any_willing_coney; # yum!
139
140       Groups can also be passed a "-suffix" argument.
141
142       Finally, if the "-as" argument to an exported routine is a reference to
143       a scalar, a reference to the routine will be placed in that scalar.
144
145   Building Subroutines to Order
146       Sometimes, you want to export things that you don't have on hand.  You
147       might want to offer customized routines built to the specification of
148       your consumer; that's just good business!  With Sub::Exporter, this is
149       easy.
150
151       To offer subroutines to order, you need to provide a generator when you
152       set up your exporter.  A generator is just a routine that returns a new
153       routine.  perlref is talking about these when it discusses closures and
154       function templates. The canonical example of a generator builds a
155       unique incrementor; here's how you'd do that with Sub::Exporter;
156
157         package Package::Counter;
158         use Sub::Exporter -setup => {
159           exports => [ counter => sub { my $i = 0; sub { $i++ } } ],
160           groups  => { default => [ qw(counter) ] },
161         };
162
163       Now anyone can use your Package::Counter module and he'll receive a
164       "counter" in his package.  It will count up by one, and will never
165       interfere with anyone else's counter.
166
167       This isn't very useful, though, unless the consumer can explain what he
168       wants.  This is done, in part, by supplying arguments when importing.
169       The following example shows how a generator can take and use arguments:
170
171         package Package::Counter;
172
173         sub _build_counter {
174           my ($class, $name, $arg) = @_;
175           $arg ||= {};
176           my $i = $arg->{start} || 0;
177           return sub { $i++ };
178         }
179
180         use Sub::Exporter -setup => {
181           exports => [ counter => \'_build_counter' ],
182           groups  => { default => [ qw(counter) ] },
183         };
184
185       Now, the consumer can (if he wants) specify a starting value for his
186       counter:
187
188         use Package::Counter counter => { start => 10 };
189
190       Arguments to a group are passed along to the generators of routines in
191       that group, but Sub::Exporter arguments -- anything beginning with a
192       dash -- are never passed in.  When groups are nested, the arguments are
193       merged as the groups are expanded.
194
195       Notice, too, that in the example above, we gave a reference to a method
196       name rather than a method implementation.  By giving the name rather
197       than the subroutine, we make it possible for subclasses of our
198       "Package::Counter" module to replace the "_build_counter" method.
199
200       When a generator is called, it is passed four parameters:
201
202       ·   the invocant on which the exporter was called
203
204       ·   the name of the export being generated (not the name it's being
205           installed as)
206
207       ·   the arguments supplied for the routine
208
209       ·   the collection of generic arguments
210
211       The fourth item is the last major feature that hasn't been covered.
212
213   Argument Collectors
214       Sometimes you will want to accept arguments once that can then be
215       available to any subroutine that you're going to export.  To do this,
216       you specify collectors, like this:
217
218         package Menu::Airline
219         use Sub::Exporter -setup => {
220           exports =>  ... ,
221           groups  =>  ... ,
222           collectors => [ qw(allergies ethics) ],
223         };
224
225       Collectors look like normal exports in the import call, but they don't
226       do anything but collect data which can later be passed to generators.
227       If the module was used like this:
228
229         use Menu::Airline allergies => [ qw(peanuts) ], ethics => [ qw(vegan) ];
230
231       ...the consumer would get a salad.  Also, all the generators would be
232       passed, as their fourth argument, something like this:
233
234         { allerges => [ qw(peanuts) ], ethics => [ qw(vegan) ] }
235
236       Generators may have arguments in their definition, as well.  These must
237       be code refs that perform validation of the collected values.  They are
238       passed the collection value and may return true or false.  If they
239       return false, the exporter will throw an exception.
240
241   Generating Many Routines in One Scope
242       Sometimes it's useful to have multiple routines generated in one scope.
243       This way they can share lexical data which is otherwise unavailable.
244       To do this, you can supply a generator for a group which returns a
245       hashref of names and code references.  This generator is passed all the
246       usual data, and the group may receive the usual "-prefix" or "-suffix"
247       arguments.
248

SEE ALSO

250       ·   Sub::Exporter for complete documentation and references to other
251           exporters
252

AUTHOR

254       Ricardo Signes <rjbs@cpan.org>
255
257       This software is copyright (c) 2007 by Ricardo Signes.
258
259       This is free software; you can redistribute it and/or modify it under
260       the same terms as the Perl 5 programming language system itself.
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264perl v5.30.1                      2020-01-30        Sub::Exporter::Tutorial(3)
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