Learning Perl Objects, References amp;amp; Modules [Electronic resources] نسخه متنی

9.6 Making a Method Work with Either Classes or Instances

All you need to fix this is a way to
detect whether the method is called on a class or an instance. The
most straightforward way to find out is with the
ref operator. This operator returns a string (the
classname) when used on a blessed reference, and
undef when used on a string (like a classname).
Modify the name method first to notice the change:

sub name {
my $either = shift;
ref $either
? $$either                # it's an instance, return name
: "an unnamed $either";   # it's a class, return generic
}

Here the
?: operator selects either the dereference or a
derived string. Now you can use it with either an instance or a
class. Note that you changed the first parameter holder to
$either to show that it is intentional:

print Horse->name, "\n";      # prints "an unnamed Horse\n"
my $tv_horse = Horse->named("Mr. Ed");
print $tv_horse->name, "\n";   # prints "Mr Ed.\n"

and now you'll fix speak to use
this:

sub speak {
my $either = shift;
print $either->name, " goes ", $either->sound, "\n";
}

Since sound already worked with either a class or
an instance, you're done!