use strict; use warnings; use Test::More tests => 6; { package Headers; use Mouse; has 'foo' => ( is => 'rw' ); } { package Response; use Mouse; use Mouse::Util::TypeConstraints; subtype 'HeadersType' => as 'Object' => where { $_->isa('Headers') }; coerce 'HeadersType' => from 'ScalarRef' => via { Headers->new(); }, from 'HashRef' => via { Headers->new(%{ $_ }); } ; has headers => ( is => 'rw', isa => 'HeadersType', coerce => 1, ); has lazy_build_coerce_headers => ( is => 'rw', isa => 'HeadersType', coerce => 1, lazy_build => 1, ); sub _build_lazy_build_coerce_headers { Headers->new(foo => 'laziness++') } has lazy_coerce_headers => ( is => 'rw', isa => 'HeadersType', coerce => 1, lazy => 1, default => sub { Headers->new(foo => 'laziness++') } ); } my $r = Response->new(headers => { foo => 'bar' }); isa_ok($r->headers, 'Headers'); is($r->headers->foo, 'bar'); $r->headers({foo => 'yay'}); isa_ok($r->headers, 'Headers'); is($r->headers->foo, 'yay'); is($r->lazy_coerce_headers->foo, 'laziness++'); is($r->lazy_build_coerce_headers->foo, 'laziness++');