use 5.010;
use MooseX::DeclareX
	plugins => [qw(preprocess postprocess)],
	;

class Joiner
{
	has separator => (is => 'rw', isa => 'Str', required => 1);
	
	method go (@strings) {
		join $self->separator => @strings;
	}	
}

role DebuggerForJoiner
{
	preprocess go (@strings) {
		map { "[$_]" } @strings
	}

	postprocess go ($result) {
		return "{$result}";
	}
}

class DebuggedJoiner
	extends Joiner
	with DebuggerForJoiner;

my $j = DebuggedJoiner->new(separator => q[ ]);
say $j->go(qw(foo bar baz));