Calls the caller's method

anazawa has asked for the wisdom of the Perl Monks concerning the following question:

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;
[download]

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;
[download]

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
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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

Comment on Calls the caller's method Select or Download Code

Replies are listed 'Best First'.
Re: Calls the caller's method by tobyink (Canon) on Jul 10, 2012 at 16:16 UTC
If you're calling a function as a method (i.e. with `->`) or calling it using a fully-qualified name (e.g. `Scalar::Util::blessed()`), then you do not need to `use` the module in question - all that is important is that it's been loaded (i.e. `use`, `require` or `do`) somewhere in this process. (And your caller has always been at least partially loaded before you were.) `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l] [select]
Re^2: Calls the caller's method by anazawa (Scribe) on Jul 10, 2012 at 17:48 UTC
Thank for your suggestion. I totally agree with you. I was blind to this issue :-)	[reply]
Re: Calls the caller's method by daxim (Curate) on Jul 10, 2012 at 15:56 UTC
When sub Bar::bar executes, the package Foo is already loaded and the symbol Foo::foo is already installed (as subroutine).	[reply]
Re^2: Calls the caller's method by anazawa (Scribe) on Jul 10, 2012 at 17:43 UTC
That makes sense. Foo::foo() is globalized, right? I remember 'our' declaration globalizes variables.	[reply]

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