NAME Safe::Isa - Call isa, can, does and DOES safely on things that may not be objects 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 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 "is_module_name" function from Module::Runtime is a good way to check for something you might be able to call methods on if you want to do that. EXPORTS $_isa $maybe_an_object->$_isa('Foo'); If called on an object, calls "isa" on it and returns the result, otherwise returns nothing. $_can $maybe_an_object->$_can('Foo'); If called on an object, calls "can" on it and returns the result, otherwise returns nothing. $_does $maybe_an_object->$_does('Foo'); If called on an object, calls "does" on it and returns the result, otherwise returns nothing. $_DOES $maybe_an_object->$_DOES('Foo'); If called on an object, calls "DOES" on it and returns the result, otherwise returns nothing. $_call_if_object $maybe_an_object->$_call_if_object(method_name => @args); If called on an object, calls "method_name" on it and returns the result, otherwise returns nothing. SEE ALSO I gave a lightning talk on this module (and curry and Import::Into) at YAPC::NA 2013 <https://www.youtube.com/watch?v=wFXWV2yY7gE&t=46m05s>. AUTHOR mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk> CONTRIBUTORS None yet. Well volunteered? :) COPYRIGHT Copyright (c) 2012 the Safe::Isa "AUTHOR" and "CONTRIBUTORS" as listed above. LICENSE This library is free software and may be distributed under the same terms as perl itself.