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Safe::Isa(3pm)        User Contributed Perl Documentation       Safe::Isa(3pm)

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 or two:

         $maybe_an_object->$_call_if_object(name => @args);
         $maybe_an_object->$_call_if_can(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.

       We are careful to make sure that scalar/list context is preserved for
       the method that is eventually called.

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. If the "does" method does not exist, returns
       nothing rather than failing.

   $_DOES
         $maybe_an_object->$_DOES('Foo');

       If called on an object, calls "DOES" on it and returns the result,
       otherwise returns nothing. On perl versions prior to 5.10.0, the built
       in core "DOES" method doesn't exist. If the method doesn't exist, this
       will fall back to calling "isa" just like the core "DOES" method.

   $_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.

   $_call_if_can
         $maybe_an_object->$_call_if_can(name => @args);

       If called on an object, calls "can" on it; if that returns true, then
       calls "method_name" on it and returns the result; if any condition is
       false 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 AT shadowcat.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.

perl v5.26.2                      2018-05-06                    Safe::Isa(3pm)