README
1NAME
2 Class::Trigger - Mixin to add / call inheritable triggers
3
4SYNOPSIS
5 package Foo;
6 use Class::Trigger;
7
8 sub foo {
9 my $self = shift;
10 $self->call_trigger('before_foo');
11 $self->do_foo;
12 $self->call_trigger('after_foo');
13 }
14
15 package main;
16 Foo->add_trigger(before_foo => \&sub1);
17 Foo->add_trigger(after_foo => \&sub2);
18
19 my $foo = Foo->new;
20 $foo->foo; # then sub1, sub2 called
21
22 # triggers are inheritable
23 package Bar;
24 use base qw(Foo);
25
26 Bar->add_trigger(before_foo => \&sub);
27
28 # triggers can be object based
29 $foo->add_hook(after_foo => \&sub3);
30 $foo->foo; # sub3 would appply only to this object
31
32DESCRIPTION
33 Class::Trigger is a mixin class to add / call triggers (or hooks) that
34 get called at some points you specify.
35
36METHODS
37 By using this module, your class is capable of following two methods.
38
39 add_trigger
40 Foo->add_trigger($triggerpoint => $sub);
41 $foo->add_trigger($triggerpoint => $sub);
42
43 Adds triggers for trigger point. You can have any number of triggers
44 for each point. Each coderef will be passed a copy of the object,
45 and return values will be ignored.
46
47 If "add_trigger" is called as object method, whole trigger table
48 will be copied onto the object. Then the object should be
49 implemented as hash.
50
51 my $foo = Foo->new;
52
53 # this trigger ($sub_foo) would apply only to $foo object
54 $foo->add_trigger($triggerpoint => $sub_foo);
55 $foo->foo;
56
57 # And not to another $bar object
58 my $bar = Foo->new;
59 $bar->foo;
60
61 call_trigger
62 $foo->call_trigger($triggerpoint);
63
64 Calls triggers for trigger point, which were added via "add_trigger"
65 method. Each triggers will be passed a copy of the object.
66
67TRIGGER POINTS
68 By default you can make any number of trigger points, but if you want to
69 declare names of trigger points explicitly, you can do it via "import".
70
71 package Foo;
72 use Class::Trigger qw(foo bar baz);
73
74 package main;
75 Foo->add_trigger(foo => \&sub1); # okay
76 Foo->add_trigger(hoge => \&sub2); # exception
77
78FAQ
79 Acknowledgement: Thanks to everyone at POOP mailing-list
80 (http://poop.sourceforge.net/).
81
82 Q. This module lets me add subs to be run before/after a specific
83 subroutine is run. Yes?
84
85 A. You put various call_trigger() method in your class. Then your class
86 users can call add_trigger() method to add subs to be run in points
87 just you specify (exactly where you put call_trigger()).
88
89 Q. Are you aware of the perl-aspects project and the Aspect module?
90 Very similar to Class::Trigger by the look of it, but its not nearly
91 as explicit. Its not necessary for foo() to actually say "triggers
92 go *here*", you just add them.
93
94 A. Yep ;)
95
96 But the difference with Aspect would be that Class::Trigger is so
97 simple that it's easy to learn, and doesn't require 5.6 or over.
98
99 Q. How does this compare to Sub::Versive, or Hook::LexWrap?
100
101 A. Very similar. But the difference with Class::Trigger would be the
102 explicitness of trigger points.
103
104 In addition, you can put hooks in any point, rather than pre or post
105 of a method.
106
107 Q. It looks interesting, but I just can't think of a practical example
108 of its use...
109
110 A. (by Tony Bowden)
111
112 I originally added code like this to Class::DBI to cope with one
113 particular case: auto-upkeep of full-text search indices.
114
115 So I added functionality in Class::DBI to be able to trigger an
116 arbitary subroutine every time something happened - then it was a
117 simple matter of setting up triggers on INSERT and UPDATE to reindex
118 that row, and on DELETE to remove that index row.
119
120 See the Class::DBI::mysql::FullTextSearch manpage and its source
121 code to see it in action.
122
123AUTHOR
124 Original idea by Tony Bowden <tony@kasei.com> in Class::DBI.
125
126 Code by Tatsuhiko Miyagawa <miyagawa@bulknews.net>.
127
128 This library is free software; you can redistribute it and/or modify it
129 under the same terms as Perl itself.
130
131SEE ALSO
132 the Class::Data::Inheritable manpage
133
134