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 # 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 $foo->foo; # sub3 would appply only to this object 33 34DESCRIPTION 35 Class::Trigger is a mixin class to add / call triggers (or hooks) that 36 get called at some points you specify. 37 38METHODS 39 By using this module, your class is capable of following two methods. 40 41 add_trigger 42 Foo->add_trigger($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 87TRIGGER 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 98FAQ 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 143AUTHOR 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 151SEE ALSO 152 Class::DBI 153 154