Belden's 2015 YAPC::NA Lightning Talk Abstract

belden-2015-lightning-talk-abstract.md

Let's say you've got this code:

{
  package math;

  sub add {
    my ($left, $right) = @_;   # Look, I am a function

    return $left + $right;
  }

  sub multiply {
    my ($class, $left, $right) = @_;  # Look, I am a method
    my $out = 0;
    $out = add($out, $left) for 1..$right;  # just humor me here
    return $out;
  }
}

This class offers both a functional (math::add) and a class interface (math->multiply). What if we wanted to make this class have a coherent interface internally, with a strange set of constraints:

1. We want to make math->multiply call any internal math:: functions as though they are methods
2. But we don't want to update those internal functions to know anything about being called as a function-or-method

That is, we don't want to do this

--- /tmp/1      2015-06-03 18:21:02.700177612 -0400
+++ /tmp/2      2015-06-03 18:20:46.928117006 -0400
@@ -2,7 +2,7 @@
   package math;
 
   sub add {
-    my ($left, $right) = @_;   # Look, I am a function
+    my (undef, $left, $right) = @_;   # Look, I am a function
 
     return $left + $right;
   }
@@ -10,7 +10,7 @@
   sub multiply {
     my ($class, $left, $right) = @_;  # Look, I am a method
     my $out = 0;
-    $out = add($out, $left) for 1..$right;  # just humor me here
+    $out = $class->add($out, $left) for 1..$right;  # just humor me here
     return $out;
   }
 }

How could we go about solving this? What weird bits of Perl might we learn along the way?