Calls the caller's method

[anazawa]

Hi Monks, I'm working on the following situation:

# Foo.pm
package Foo;
use strict;
use warnings;
use Bar;

sub foo { warn 'Foo::foo was called' }

Bar->bar;

1;

A package Foo calls Bar's bar() method. Foo defines foo() method which prints a message to STDERR. On the other hand, Bar.pm looks as follows:

# Bar.pm
package Bar;
use strict;
use warnings;

sub bar { Foo->foo }

1;

Bar defines bar() method which calls Foo's foo() method. I executed Foo.pm and confirmed the script output 'Foo::foo was called':

$ ls
Foo.pm Bar.pm
$ perl Foo.pm
Foo::foo was called

This result shows us that Bar can call Foo's foo() method without loading Foo.pm (I mean, without 'use Foo;') In other words, Bar can call the caller's method ( Foo::foo() ). If so, why is this possible? Is this one of well-known specifications? Which perldoc helps me understand this result?

Sincerely,
Ryo