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1 | package Safe::Isa; |
2 | |
3 | use strict; |
4 | use warnings FATAL => 'all'; |
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5 | use Scalar::Util (); |
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6 | use Exporter 5.57 qw(import); |
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7 | |
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8 | our $VERSION = '1.000008'; |
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9 | |
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10 | our @EXPORT = qw($_call_if_object $_isa $_can $_does $_DOES $_call_if_can); |
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11 | |
12 | our $_call_if_object = sub { |
13 | my ($obj, $method) = (shift, shift); |
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14 | # This is intentionally a truth test, not a defined test, otherwise |
15 | # we gratuitously break modules like Scalar::Defer, which would be |
16 | # un-perlish. |
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17 | return unless Scalar::Util::blessed($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 | our $_call_if_can = sub { |
28 | my ($obj, $method) = (shift, shift); |
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29 | return unless $obj->$_call_if_object(can => $method); |
30 | return $obj->$method(@_); |
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31 | }; |
32 | |
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33 | 1; |
34 | __END__ |
35 | |
36 | =pod |
37 | |
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38 | =head1 NAME |
39 | |
40 | Safe::Isa - Call isa, can, does and DOES safely on things that may not be objects |
41 | |
42 | =head1 SYNOPSIS |
43 | |
44 | use strict; |
45 | use warnings; |
46 | |
47 | { package Foo; sub new { bless({}, $_[0]) } } |
48 | { package Bar; our @ISA = qw(Foo); sub bar { 1 } } |
49 | |
50 | my $foo = Foo->new; |
51 | my $bar = Bar->new; |
52 | my $blam = [ 42 ]; |
53 | |
54 | # basic isa usage - |
55 | |
56 | $foo->isa('Foo'); # true |
57 | $bar->isa('Foo'); # true |
58 | $blam->isa('Foo'); # BOOM |
59 | |
60 | $foo->can('bar'); # false |
61 | $bar->can('bar'); # true |
62 | $blam->can('bar'); # BOOM |
63 | |
64 | # Safe::Isa usage - |
65 | |
66 | use Safe::Isa; |
67 | |
68 | $foo->$_isa('Foo'); # true |
69 | $bar->$_isa('Foo'); # true |
70 | $blam->$_isa('Foo'); # false, no boom today |
71 | |
72 | $foo->$_can('bar'); # false |
73 | $bar->$_can('bar'); # true |
74 | $blam->$_can('bar'); # false, no boom today |
75 | |
76 | Similarly: |
77 | |
78 | $maybe_an_object->$_does('RoleName'); # true or false, no boom today |
79 | $maybe_an_object->$_DOES('RoleName'); # true or false, no boom today |
80 | |
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81 | And just in case we missed a method or two: |
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82 | |
83 | $maybe_an_object->$_call_if_object(name => @args); |
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84 | $maybe_an_object->$_call_if_can(name => @args); |
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85 | |
86 | Or to re-use a previous example for purposes of explication: |
87 | |
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88 | $foo->$_call_if_object(isa => 'Foo'); # true |
89 | $bar->$_call_if_object(isa => 'Foo'); # true |
90 | $blam->$_call_if_object(isa => 'Foo'); # false, no boom today |
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91 | |
92 | =head1 DESCRIPTION |
93 | |
94 | How many times have you found yourself writing: |
95 | |
96 | if ($obj->isa('Something')) { |
97 | |
98 | and then shortly afterwards cursing and changing it to: |
99 | |
100 | if (Scalar::Util::blessed($obj) and $obj->isa('Something')) { |
101 | |
102 | Right. That's why this module exists. |
103 | |
104 | Since perl allows us to provide a subroutine reference or a method name to |
105 | the -> operator when used as a method call, and a subroutine doesn't require |
106 | the invocant to actually be an object, we can create safe versions of isa, |
107 | can and friends by using a subroutine reference that only tries to call the |
108 | method if it's used on an object. So: |
109 | |
110 | my $isa_Foo = $maybe_an_object->$_call_if_object(isa => 'Foo'); |
111 | |
112 | is equivalent to |
113 | |
114 | my $isa_Foo = do { |
115 | if (Scalar::Util::blessed($maybe_an_object)) { |
116 | $maybe_an_object->isa('Foo'); |
117 | } else { |
118 | undef; |
119 | } |
120 | }; |
121 | |
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122 | Note that we don't handle trying class names, because many things are valid |
123 | class names that you might not want to treat as one (like say "Matt") - the |
124 | C<is_module_name> function from L<Module::Runtime> is a good way to check for |
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125 | something you might be able to call methods on if you want to do that. |
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126 | |
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127 | We are careful to make sure that scalar/list context is preserved for the |
128 | method that is eventually called. |
129 | |
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130 | =head1 EXPORTS |
131 | |
132 | =head2 $_isa |
133 | |
134 | $maybe_an_object->$_isa('Foo'); |
135 | |
136 | If called on an object, calls C<isa> on it and returns the result, otherwise |
137 | returns nothing. |
138 | |
139 | =head2 $_can |
140 | |
141 | $maybe_an_object->$_can('Foo'); |
142 | |
143 | If called on an object, calls C<can> on it and returns the result, otherwise |
144 | returns nothing. |
145 | |
146 | =head2 $_does |
147 | |
148 | $maybe_an_object->$_does('Foo'); |
149 | |
150 | If called on an object, calls C<does> on it and returns the result, otherwise |
151 | returns nothing. |
152 | |
153 | =head2 $_DOES |
154 | |
155 | $maybe_an_object->$_DOES('Foo'); |
156 | |
157 | If called on an object, calls C<DOES> on it and returns the result, otherwise |
158 | returns nothing. |
159 | |
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160 | =head2 $_call_if_object |
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161 | |
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162 | $maybe_an_object->$_call_if_object(method_name => @args); |
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163 | |
164 | If called on an object, calls C<method_name> on it and returns the result, |
165 | otherwise returns nothing. |
166 | |
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167 | =head2 $_call_if_can |
168 | |
169 | $maybe_an_object->$_call_if_can(name => @args); |
170 | |
171 | If called on an object, calls C<can> on it; if that returns true, then |
172 | calls C<method_name> on it and returns the result; if any condition is false |
173 | returns nothing. |
174 | |
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175 | =head1 SEE ALSO |
176 | |
177 | I gave a lightning talk on this module (and L<curry> and L<Import::Into>) at |
178 | L<YAPC::NA 2013|https://www.youtube.com/watch?v=wFXWV2yY7gE&t=46m05s>. |
179 | |
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180 | =head1 AUTHOR |
181 | |
182 | mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk> |
183 | |
184 | =head1 CONTRIBUTORS |
185 | |
186 | None yet. Well volunteered? :) |
187 | |
188 | =head1 COPYRIGHT |
189 | |
190 | Copyright (c) 2012 the Safe::Isa L</AUTHOR> and L</CONTRIBUTORS> |
191 | as listed above. |
192 | |
193 | =head1 LICENSE |
194 | |
195 | This library is free software and may be distributed under the same terms |
196 | as perl itself. |
197 | |
198 | =cut |