I must say as a premise that I'm not keen myself on indirect object notation, and I've at best seldom adopted it, if ever.

However, it occured to me a case in which for some reason it would have seemed natural for me to use it. Trimmed down to an absolute minimum suppose I have a class Foo: 

# -*- Perl -*-
package Foo;

use strict;
use warnings;

sub new { bless [], shift }
    
sub warn { shift; warn "[", __PACKAGE__, "] ", @_ }

sub do_cb {
    my ($self, $cb)=@_;
    $self->$cb;
}

1;

__END__

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Such that the do_cb method accepts and runs a callback. Now, if I use it like thus: 
#!/usr/bin/perl

use strict;
use warnings;
use Foo;

my $f=Foo->new;

$f->do_cb(sub {
    my $caller=shift;
    $caller->warn("no good for me\n");
});

__END__

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then everything is fine. But if I try 
    warn $caller "no good for me\n";

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instead, it doesn't work due to warn() being a builtin function. Incidentally, the latter form seems quite expressive to me in terms of message passing to the "caller" object.

So leaving aside for the moment any argument about how {risky,dangerous,error-prone,whatever} this could be (for I'm aware about them - and please do not point out I can call it "Warn" either, for I know that too), is it first of all possible, some way or another? (Especially given that in perl I can even replace most builtins with my own subs.)

UPDATE: Fixed a "minor but relevant" bug! (Thanks to Fletch.)

In reply to Speaking of indirect object notation... by blazar

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