root/Class-Trigger/trunk/README

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merged Jesse's return values branch

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1 NAME
2     Class::Trigger - Mixin to add / call inheritable triggers
3
4 SYNOPSIS
5       package Foo;
6       use Class::Trigger;
7
8       sub foo {
9           my $self = shift;
10           $self->call_trigger('before_foo');
11           # some code ...
12           $self->call_trigger('middle_of_foo');
13           # some code ...
14           $self->call_trigger('after_foo');
15       }
16
17       package main;
18       Foo->add_trigger(before_foo => \&sub1);
19       Foo->add_trigger(after_foo => \&sub2);
20
21       my $foo = Foo->new;
22       $foo->foo;            # then sub1, sub2 called
23
24       # triggers are inheritable
25       package Bar;
26       use base qw(Foo);
27
28       Bar->add_trigger(before_foo => \&sub);
29
30       # triggers can be object based
31       $foo->add_trigger(after_foo => \&sub3);
32       $foo->foo;            # sub3 would appply only to this object
33
34 DESCRIPTION
35     Class::Trigger is a mixin class to add / call triggers (or hooks) that
36     get called at some points you specify.
37
38 METHODS
39     By using this module, your class is capable of following two methods.
40
41     add_trigger
42           Foo->add_trigger($triggerpoint => $sub);
43           $foo->add_trigger($triggerpoint => $sub);
44
45           Foo->add_trigger( name => $triggerpoint,
46                             callback => sub {return undef},
47                             abortable => 1);
48
49           # no further triggers will be called. Undef will be returned.
50
51         Adds triggers for trigger point. You can have any number of triggers
52         for each point. Each coderef will be passed a reference to the
53         calling object, as well as arguments passed in via run_trigger.
54
55         If add_trigger is called with named_parameters and the "abortable"
56         parameter is passed a true value, a false return values will stop
57         processing of this trigger point. If the trigger is "abortable"
58         return the return value from the last callback processed will be
59         returned to calling code.
60
61         If "add_trigger" is called without the "abortable" flag, return
62         values will be ignored.
63
64         If "add_trigger" is called as object method, whole current trigger
65         table will be copied onto the object and the new trigger added to
66         that. (The object must be implemented as hash.)
67
68           my $foo = Foo->new;
69
70           # this trigger ($sub_foo) would apply only to $foo object
71           $foo->add_trigger($triggerpoint => $sub_foo);
72           $foo->foo;
73
74           # And not to another $bar object
75           my $bar = Foo->new;
76           $bar->foo;
77
78     call_trigger
79           $foo->call_trigger($triggerpoint, @args);
80
81         Calls triggers for trigger point, which were added via "add_trigger"
82         method. Each triggers will be passed a copy of the object as the
83         first argument. Remaining arguments passed to "call_trigger" will be
84         passed on to each trigger. Triggers are invoked in the same order
85         they were defined.
86
87 TRIGGER POINTS
88     By default you can make any number of trigger points, but if you want to
89     declare names of trigger points explicitly, you can do it via "import".
90
91       package Foo;
92       use Class::Trigger qw(foo bar baz);
93
94       package main;
95       Foo->add_trigger(foo  => \&sub1); # okay
96       Foo->add_trigger(hoge => \&sub2); # exception
97
98 FAQ
99     Acknowledgement: Thanks to everyone at POOP mailing-list
100     (http://poop.sourceforge.net/).
101
102     Q.  This module lets me add subs to be run before/after a specific
103         subroutine is run. Yes?
104
105     A.  You put various call_trigger() method in your class. Then your class
106         users can call add_trigger() method to add subs to be run in points
107         just you specify (exactly where you put call_trigger()).
108
109     Q.  Are you aware of the perl-aspects project and the Aspect module?
110         Very similar to Class::Trigger by the look of it, but its not nearly
111         as explicit. Its not necessary for foo() to actually say "triggers
112         go *here*", you just add them.
113
114     A.  Yep ;)
115
116         But the difference with Aspect would be that Class::Trigger is so
117         simple that it's easy to learn, and doesn't require 5.6 or over.
118
119     Q.  How does this compare to Sub::Versive, or Hook::LexWrap?
120
121     A.  Very similar. But the difference with Class::Trigger would be the
122         explicitness of trigger points.
123
124         In addition, you can put hooks in any point, rather than pre or post
125         of a method.
126
127     Q.  It looks interesting, but I just can't think of a practical example
128         of its use...
129
130     A.  (by Tony Bowden)
131
132         I originally added code like this to Class::DBI to cope with one
133         particular case: auto-upkeep of full-text search indices.
134
135         So I added functionality in Class::DBI to be able to trigger an
136         arbitary subroutine every time something happened - then it was a
137         simple matter of setting up triggers on INSERT and UPDATE to reindex
138         that row, and on DELETE to remove that index row.
139
140         See Class::DBI::mysql::FullTextSearch and its source code to see it
141         in action.
142
143 AUTHOR
144     Original idea by Tony Bowden <tony@kasei.com> in Class::DBI.
145
146     Code by Tatsuhiko Miyagawa <miyagawa@bulknews.net>.
147
148     This library is free software; you can redistribute it and/or modify it
149     under the same terms as Perl itself.
150
151 SEE ALSO
152     Class::DBI
153
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