Safe::Isa - Call isa, can, does and DOES safely on things that may not be objects
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
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.
is_module_name
$maybe_an_object->$_isa('Foo');
If called on an object, calls isa on it and returns the result, otherwise returns nothing.
isa
$maybe_an_object->$_can('Foo');
If called on an object, calls can on it and returns the result, otherwise returns nothing.
can
$maybe_an_object->$_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.
DOES
$maybe_an_object->$_call_if_object(method_name => @args);
If called on an object, calls method_name on it and returns the result, otherwise returns nothing.
method_name
I gave a lightning talk on this module (and curry and Import::Into) at YAPC::NA 2013.
mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk>
None yet. Well volunteered? :)
Copyright (c) 2012 the Safe::Isa "AUTHOR" and "CONTRIBUTORS" as listed above.
This library is free software and may be distributed under the same terms as perl itself.
To install Safe::Isa, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Safe::Isa
CPAN shell
perl -MCPAN -e shell install Safe::Isa
For more information on module installation, please visit the detailed CPAN module installation guide.