When Moose sees this:

has 'successor' => (
    is => 'rw',
    isa => 'ChainOfResposibilityIf',
);
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If the ChainOfResposibilityIf role has not yet been loaded (use/require), Moose needs to make a snap decision about what kind of thing ChainOfResposibilityIf is. It needs to set up everything for the attribute straight away - it doesn't wait until you actully make use of the attribute.

Anyway, Moose guesses that it's a class. So later, when you assign to the attribute, it checks $value->isa('ChainOfResposibilityIf') (which fails) instead of $value->DOES('ChainOfResposibilityIf') (which would pass).

Three possible solutions. Any of them will do:

• Load ChainOfResposibilityIf earlier. Before using it in an attribute definition. (This seems the most fragile solution to me, and is my least preferred, but it should work.)

• Instead of isa use does:

  has 'successor' => (
      is => 'rw',
      does => 'ChainOfResposibilityIf', # !!!
  );
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• Create an explicit type constraint object, and pass that to isa instead of passing the string "ChainOfResposibilityIf":

  use Moose::Util::TypeConstraints qw(role_type);
  has 'successor' => (
      is => 'rw',
      isa => role_type('ChainOfResposibilityIf'),
  );
  [download]