/usr/share/perl5/Safe/Isa.pm is in libsafe-isa-perl 1.000005-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 | package Safe::Isa;
use strict;
use warnings FATAL => 'all';
use Scalar::Util qw(blessed);
use Exporter 5.57 qw(import);
our $VERSION = '1.000005';
our @EXPORT = qw($_call_if_object $_isa $_can $_does $_DOES);
our $_call_if_object = sub {
my ($obj, $method) = (shift, shift);
# This is intentionally a truth test, not a defined test, otherwise
# we gratuitously break modules like Scalar::Defer, which would be
# un-perlish.
return unless blessed($obj);
return $obj->$method(@_);
};
our ($_isa, $_can, $_does, $_DOES) = map {
my $method = $_;
sub { my $obj = shift; $obj->$_call_if_object($method => @_) }
} qw(isa can does DOES);
=head1 NAME
Safe::Isa - Call isa, can, does and DOES safely on things that may not be objects
=head1 SYNOPSIS
use strict;
use warnings;
{ package Foo; sub new { bless({}, $_[0]) } }
{ package Bar; our @ISA = qw(Foo); sub bar { 1 } }
my $foo = Foo->new;
my $bar = Bar->new;
my $blam = [ 42 ];
# basic isa usage -
$foo->isa('Foo'); # true
$bar->isa('Foo'); # true
$blam->isa('Foo'); # BOOM
$foo->can('bar'); # false
$bar->can('bar'); # true
$blam->can('bar'); # BOOM
# Safe::Isa usage -
use Safe::Isa;
$foo->$_isa('Foo'); # true
$bar->$_isa('Foo'); # true
$blam->$_isa('Foo'); # false, no boom today
$foo->$_can('bar'); # false
$bar->$_can('bar'); # true
$blam->$_can('bar'); # false, no boom today
Similarly:
$maybe_an_object->$_does('RoleName'); # true or false, no boom today
$maybe_an_object->$_DOES('RoleName'); # true or false, no boom today
And just in case we missed a method:
$maybe_an_object->$_call_if_object(name => @args);
Or to re-use a previous example for purposes of explication:
$foo->$_call_if_object(isa => 'Foo'); # true
$bar->$_call_if_object(isa => 'Foo'); # true
$blam->$_call_if_object(isa => 'Foo'); # false, no boom today
=head1 DESCRIPTION
How many times have you found yourself writing:
if ($obj->isa('Something')) {
and then shortly afterwards cursing and changing it to:
if (Scalar::Util::blessed($obj) and $obj->isa('Something')) {
Right. That's why this module exists.
Since perl allows us to provide a subroutine reference or a method name to
the -> operator when used as a method call, and a subroutine doesn't require
the invocant to actually be an object, we can create safe versions of isa,
can and friends by using a subroutine reference that only tries to call the
method if it's used on an object. So:
my $isa_Foo = $maybe_an_object->$_call_if_object(isa => 'Foo');
is equivalent to
my $isa_Foo = do {
if (Scalar::Util::blessed($maybe_an_object)) {
$maybe_an_object->isa('Foo');
} else {
undef;
}
};
Note that we don't handle trying class names, because many things are valid
class names that you might not want to treat as one (like say "Matt") - the
C<is_module_name> function from L<Module::Runtime> is a good way to check for
something you might be able to call methods on if you want to do that.
=head1 EXPORTS
=head2 $_isa
$maybe_an_object->$_isa('Foo');
If called on an object, calls C<isa> on it and returns the result, otherwise
returns nothing.
=head2 $_can
$maybe_an_object->$_can('Foo');
If called on an object, calls C<can> on it and returns the result, otherwise
returns nothing.
=head2 $_does
$maybe_an_object->$_does('Foo');
If called on an object, calls C<does> on it and returns the result, otherwise
returns nothing.
=head2 $_DOES
$maybe_an_object->$_DOES('Foo');
If called on an object, calls C<DOES> on it and returns the result, otherwise
returns nothing.
=head2 $_call_if_object
$maybe_an_object->$_call_if_object(method_name => @args);
If called on an object, calls C<method_name> on it and returns the result,
otherwise returns nothing.
=head1 SEE ALSO
I gave a lightning talk on this module (and L<curry> and L<Import::Into>) at
L<YAPC::NA 2013|https://www.youtube.com/watch?v=wFXWV2yY7gE&t=46m05s>.
=head1 AUTHOR
mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk>
=head1 CONTRIBUTORS
None yet. Well volunteered? :)
=head1 COPYRIGHT
Copyright (c) 2012 the Safe::Isa L</AUTHOR> and L</CONTRIBUTORS>
as listed above.
=head1 LICENSE
This library is free software and may be distributed under the same terms
as perl itself.
=cut
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