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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 $VERSION = '1.000004'; |
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9 | |
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10 | our @EXPORT = qw($_call_if_object $_call_if_object_or_classname $_isa $_can $_does $_DOES); |
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11 | |
12 | our $_call_if_object = sub { |
13 | my ($obj, $method) = (shift, shift); |
14 | return unless blessed($obj); |
15 | return $obj->$method(@_); |
16 | }; |
17 | |
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18 | our $_call_if_object_or_classname = sub { |
19 | my ($thing, $method) = (shift, shift); |
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20 | return unless blessed($thing) or defined($thing) and do { |
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21 | no strict 'refs'; |
22 | %{"main::${thing}::"} |
23 | }; |
24 | return $thing->$method(@_); |
25 | }; |
26 | |
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27 | our ($_isa, $_can, $_does, $_DOES) = map { |
28 | my $method = $_; |
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29 | sub { my $obj = shift; $obj->$_call_if_object_or_classname($method => @_) } |
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30 | } qw(isa can does DOES); |
31 | |
32 | =head1 NAME |
33 | |
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34 | Safe::Isa - Call isa, can, does and DOES safely on arbitrary things |
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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; |
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46 | my $class = 'Bar'; |
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47 | my $blam = [ 42 ]; |
48 | |
49 | # basic isa usage - |
50 | |
51 | $foo->isa('Foo'); # true |
52 | $bar->isa('Foo'); # true |
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53 | $class->isa('Foo') # true |
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54 | $blam->isa('Foo'); # BOOM |
55 | |
56 | $foo->can('bar'); # false |
57 | $bar->can('bar'); # true |
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58 | $class->can('bar); # true |
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59 | $blam->can('bar'); # BOOM |
60 | |
61 | # Safe::Isa usage - |
62 | |
63 | use Safe::Isa; |
64 | |
65 | $foo->$_isa('Foo'); # true |
66 | $bar->$_isa('Foo'); # true |
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67 | $class->isa('Foo') # true |
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68 | $blam->$_isa('Foo'); # false, no boom today |
69 | |
70 | $foo->$_can('bar'); # false |
71 | $bar->$_can('bar'); # true |
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72 | $class->can('bar); # true |
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73 | $blam->$_can('bar'); # false, no boom today |
74 | |
75 | Similarly: |
76 | |
77 | $maybe_an_object->$_does('RoleName'); # true or false, no boom today |
78 | $maybe_an_object->$_DOES('RoleName'); # true or false, no boom today |
79 | |
80 | And just in case we missed a method: |
81 | |
82 | $maybe_an_object->$_call_if_object(name => @args); |
83 | |
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84 | or this might be closer to what you want: |
85 | |
86 | $maybe_a_referent->$_call_if_object_or_class(name => @args); |
87 | |
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88 | Or to re-use a previous example for purposes of explication: |
89 | |
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90 | $foo->$_call_if_object(isa => 'Foo'); # true |
91 | $bar->$_call_if_object(isa => 'Foo'); # true |
92 | $blam->$_call_if_object(isa => 'Foo'); # false, no boom today |
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93 | |
94 | =head1 DESCRIPTION |
95 | |
96 | How many times have you found yourself writing: |
97 | |
98 | if ($obj->isa('Something')) { |
99 | |
100 | and then shortly afterwards cursing and changing it to: |
101 | |
102 | if (Scalar::Util::blessed($obj) and $obj->isa('Something')) { |
103 | |
104 | Right. That's why this module exists. |
105 | |
106 | Since perl allows us to provide a subroutine reference or a method name to |
107 | the -> operator when used as a method call, and a subroutine doesn't require |
108 | the invocant to actually be an object, we can create safe versions of isa, |
109 | can and friends by using a subroutine reference that only tries to call the |
110 | method if it's used on an object. So: |
111 | |
112 | my $isa_Foo = $maybe_an_object->$_call_if_object(isa => 'Foo'); |
113 | |
114 | is equivalent to |
115 | |
116 | my $isa_Foo = do { |
117 | if (Scalar::Util::blessed($maybe_an_object)) { |
118 | $maybe_an_object->isa('Foo'); |
119 | } else { |
120 | undef; |
121 | } |
122 | }; |
123 | |
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124 | Note that we don't handle trying class names, because many things are valid |
125 | class names that you might not want to treat as one (like say "Matt") - the |
126 | C<is_module_name> function from L<Module::Runtime> is a good way to check for |
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127 | something you might be able to call methods on if you want to do that. |
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128 | |
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129 | =head1 EXPORTS |
130 | |
131 | =head2 $_isa |
132 | |
133 | $maybe_an_object->$_isa('Foo'); |
134 | |
135 | If called on an object, calls C<isa> on it and returns the result, otherwise |
136 | returns nothing. |
137 | |
138 | =head2 $_can |
139 | |
140 | $maybe_an_object->$_can('Foo'); |
141 | |
142 | If called on an object, calls C<can> on it and returns the result, otherwise |
143 | returns nothing. |
144 | |
145 | =head2 $_does |
146 | |
147 | $maybe_an_object->$_does('Foo'); |
148 | |
149 | If called on an object, calls C<does> on it and returns the result, otherwise |
150 | returns nothing. |
151 | |
152 | =head2 $_DOES |
153 | |
154 | $maybe_an_object->$_DOES('Foo'); |
155 | |
156 | If called on an object, calls C<DOES> on it and returns the result, otherwise |
157 | returns nothing. |
158 | |
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159 | =head2 $_call_if_object |
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160 | |
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161 | $maybe_an_object->$_call_if_object(method_name => @args); |
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162 | |
163 | If called on an object, calls C<method_name> on it and returns the result, |
164 | otherwise returns nothing. |
165 | |
166 | =head1 AUTHOR |
167 | |
168 | mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk> |
169 | |
170 | =head1 CONTRIBUTORS |
171 | |
172 | None yet. Well volunteered? :) |
173 | |
174 | =head1 COPYRIGHT |
175 | |
176 | Copyright (c) 2012 the Safe::Isa L</AUTHOR> and L</CONTRIBUTORS> |
177 | as listed above. |
178 | |
179 | =head1 LICENSE |
180 | |
181 | This library is free software and may be distributed under the same terms |
182 | as perl itself. |
183 | |
184 | =cut |