Here is a sample class to be used to illustrate the possible solutions and show the specific issues of the problem:

use 5.10.1;
use utf8;

package C;   # main class with user-facing API
use Moose;
use MooseX::Method::Signatures;

method foo (Str $x)
 {
 say "Called original foo($x).";
 }

 
method build_c2
 {
 return C::C2->new;
 }
 
has c2 => (
   is => 'rw',
   handles => [ 'bar' ],
   builder => 'build_c2',
   lazy => 1
   );


method build_c3
 {
 return C::C3->new;
 }
 
has c3 => (
   is => 'rw',
   handles => [ 'baz' ],
   builder => 'build_c3',
   lazy => 1
   );

   
# ==================

package C::C2;  # a helper class
use Moose;
use MooseX::Method::Signatures;

method bar (Str $x)
 {
 say "Called original bar($x).";
 }
 
# ==================

package C::C3;  # a helper class
use Moose;
use MooseX::Method::Signatures;

method baz (Str $x)
 {
 say "Called original baz($x).";
 }
 
# ==================

package main;
 
my $c= C->new;
 
$c->foo (1);
$c->bar (2);
$c->baz (3);
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Now, lets say we have extensions to C. In order to work, an extension needs to hook the methods foo, bar, and baz. By "hook" I mean it can override or use before/after/around modifiers of some kind.

As you can see, the methods are spread out over three different classes (albeit in a simple way). I've also made the attributes "rw' for ease in solving the problem.

Approach 1: run-time patching (traits)

A call to install an extension can apply a run-time role to $c, and also apply roles to $c->c2 and $c->c3. But that is evil "run time" patching...

Approach 2: apply before creating

Using the proper pedigreed MooseX::Traits and calling $c= C->with_traits(qw/ext1 ext2/)->new will apply the role ext1 and ext2 to C, and then call new. But that only fixes foo. How does it make C-with-roles apply the roles to C2 and C3 as well? For a single extension, it can override the builders. That's why this example shows two roles: they have to play together. Only after all roles are applied can it know what to create.

How would you do that?