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1 | package Safe::Isa; |
2 | |
3 | use strict; |
4 | use warnings FATAL => 'all'; |
5 | use Scalar::Util qw(blessed); |
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6 | use Exporter 5.57 qw(import); |
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7 | |
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8 | our $VERSION = '1.000005'; |
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9 | |
10 | our @EXPORT = qw($_call_if_object $_isa $_can $_does $_DOES); |
11 | |
12 | our $_call_if_object = sub { |
13 | my ($obj, $method) = (shift, shift); |
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14 | # This is intentionally a truth test, not a defined test, otherwise |
15 | # we gratuitously break modules like Scalar::Defer, which would be |
16 | # un-perlish. |
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17 | return unless blessed($obj); |
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18 | return $obj->isa(@_) if lc($method) eq 'does' and not $obj->can($method); |
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19 | return $obj->$method(@_); |
20 | }; |
21 | |
22 | our ($_isa, $_can, $_does, $_DOES) = map { |
23 | my $method = $_; |
24 | sub { my $obj = shift; $obj->$_call_if_object($method => @_) } |
25 | } qw(isa can does DOES); |
26 | |
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27 | 1; |
28 | __END__ |
29 | |
30 | =pod |
31 | |
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32 | =head1 NAME |
33 | |
34 | Safe::Isa - Call isa, can, does and DOES safely on things that may not be objects |
35 | |
36 | =head1 SYNOPSIS |
37 | |
38 | use strict; |
39 | use warnings; |
40 | |
41 | { package Foo; sub new { bless({}, $_[0]) } } |
42 | { package Bar; our @ISA = qw(Foo); sub bar { 1 } } |
43 | |
44 | my $foo = Foo->new; |
45 | my $bar = Bar->new; |
46 | my $blam = [ 42 ]; |
47 | |
48 | # basic isa usage - |
49 | |
50 | $foo->isa('Foo'); # true |
51 | $bar->isa('Foo'); # true |
52 | $blam->isa('Foo'); # BOOM |
53 | |
54 | $foo->can('bar'); # false |
55 | $bar->can('bar'); # true |
56 | $blam->can('bar'); # BOOM |
57 | |
58 | # Safe::Isa usage - |
59 | |
60 | use Safe::Isa; |
61 | |
62 | $foo->$_isa('Foo'); # true |
63 | $bar->$_isa('Foo'); # true |
64 | $blam->$_isa('Foo'); # false, no boom today |
65 | |
66 | $foo->$_can('bar'); # false |
67 | $bar->$_can('bar'); # true |
68 | $blam->$_can('bar'); # false, no boom today |
69 | |
70 | Similarly: |
71 | |
72 | $maybe_an_object->$_does('RoleName'); # true or false, no boom today |
73 | $maybe_an_object->$_DOES('RoleName'); # true or false, no boom today |
74 | |
75 | And just in case we missed a method: |
76 | |
77 | $maybe_an_object->$_call_if_object(name => @args); |
78 | |
79 | Or to re-use a previous example for purposes of explication: |
80 | |
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81 | $foo->$_call_if_object(isa => 'Foo'); # true |
82 | $bar->$_call_if_object(isa => 'Foo'); # true |
83 | $blam->$_call_if_object(isa => 'Foo'); # false, no boom today |
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84 | |
85 | =head1 DESCRIPTION |
86 | |
87 | How many times have you found yourself writing: |
88 | |
89 | if ($obj->isa('Something')) { |
90 | |
91 | and then shortly afterwards cursing and changing it to: |
92 | |
93 | if (Scalar::Util::blessed($obj) and $obj->isa('Something')) { |
94 | |
95 | Right. That's why this module exists. |
96 | |
97 | Since perl allows us to provide a subroutine reference or a method name to |
98 | the -> operator when used as a method call, and a subroutine doesn't require |
99 | the invocant to actually be an object, we can create safe versions of isa, |
100 | can and friends by using a subroutine reference that only tries to call the |
101 | method if it's used on an object. So: |
102 | |
103 | my $isa_Foo = $maybe_an_object->$_call_if_object(isa => 'Foo'); |
104 | |
105 | is equivalent to |
106 | |
107 | my $isa_Foo = do { |
108 | if (Scalar::Util::blessed($maybe_an_object)) { |
109 | $maybe_an_object->isa('Foo'); |
110 | } else { |
111 | undef; |
112 | } |
113 | }; |
114 | |
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115 | Note that we don't handle trying class names, because many things are valid |
116 | class names that you might not want to treat as one (like say "Matt") - the |
117 | C<is_module_name> function from L<Module::Runtime> is a good way to check for |
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118 | something you might be able to call methods on if you want to do that. |
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119 | |
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120 | =head1 EXPORTS |
121 | |
122 | =head2 $_isa |
123 | |
124 | $maybe_an_object->$_isa('Foo'); |
125 | |
126 | If called on an object, calls C<isa> on it and returns the result, otherwise |
127 | returns nothing. |
128 | |
129 | =head2 $_can |
130 | |
131 | $maybe_an_object->$_can('Foo'); |
132 | |
133 | If called on an object, calls C<can> on it and returns the result, otherwise |
134 | returns nothing. |
135 | |
136 | =head2 $_does |
137 | |
138 | $maybe_an_object->$_does('Foo'); |
139 | |
140 | If called on an object, calls C<does> on it and returns the result, otherwise |
141 | returns nothing. |
142 | |
143 | =head2 $_DOES |
144 | |
145 | $maybe_an_object->$_DOES('Foo'); |
146 | |
147 | If called on an object, calls C<DOES> on it and returns the result, otherwise |
148 | returns nothing. |
149 | |
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150 | =head2 $_call_if_object |
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151 | |
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152 | $maybe_an_object->$_call_if_object(method_name => @args); |
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153 | |
154 | If called on an object, calls C<method_name> on it and returns the result, |
155 | otherwise returns nothing. |
156 | |
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157 | =head1 SEE ALSO |
158 | |
159 | I gave a lightning talk on this module (and L<curry> and L<Import::Into>) at |
160 | L<YAPC::NA 2013|https://www.youtube.com/watch?v=wFXWV2yY7gE&t=46m05s>. |
161 | |
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162 | =head1 AUTHOR |
163 | |
164 | mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk> |
165 | |
166 | =head1 CONTRIBUTORS |
167 | |
168 | None yet. Well volunteered? :) |
169 | |
170 | =head1 COPYRIGHT |
171 | |
172 | Copyright (c) 2012 the Safe::Isa L</AUTHOR> and L</CONTRIBUTORS> |
173 | as listed above. |
174 | |
175 | =head1 LICENSE |
176 | |
177 | This library is free software and may be distributed under the same terms |
178 | as perl itself. |
179 | |
180 | =cut |