--- /dev/null
+use strict;
+use warnings;
+use Test::More tests => 13;
+
+{
+ package Response::Headers;
+ use Mouse;
+ has 'foo' => ( is => 'rw' );
+}
+{
+ package Request::Headers;
+ use Mouse;
+ has 'foo' => ( is => 'rw' );
+}
+
+{
+ package Response;
+ use Mouse;
+ use Mouse::Util::TypeConstraints;
+
+ subtype 'Headers' => as 'Object', where { $_->isa('Response::Headers') };
+ coerce 'Headers' =>
+ from 'HashRef' => via {
+ Response::Headers->new(%{ $_ });
+ },
+ ;
+
+ has headers => (
+ is => 'rw',
+ isa => 'Headers',
+ coerce => 1,
+ );
+}
+
+eval {
+ package Request;
+ use Mouse::Util::TypeConstraints;
+
+ type 'Headers' => where { defined $_ && eval { $_->isa('Request::Headers') } };
+};
+like $@, qr/The type constraint 'Headers' has already been created in Response and cannot be created again in Request/;
+
+eval {
+ package Request;
+ use Mouse::Util::TypeConstraints;
+
+ coerce 'TooBad' =>
+ from 'HashRef' => via {
+ Request::Headers->new(%{ $_ });
+ },
+ ;
+};
+like $@, qr/Cannot find type 'TooBad', perhaps you forgot to load it./;
+
+eval {
+ package Request;
+ use Mouse::Util::TypeConstraints;
+
+ coerce 'Headers' =>
+ from 'HashRef' => via {
+ Request::Headers->new(%{ $_ });
+ },
+ ;
+};
+like $@, qr/A coercion action already exists for 'HashRef'/;
+
+eval {
+ package Request;
+ use Mouse::Util::TypeConstraints;
+
+ coerce 'Int' =>
+ from 'XXX' => via {
+ 1
+ },
+ ;
+};
+like $@, qr/Could not find the type constraint \(XXX\) to coerce from/;
+
+eval {
+ package Request;
+ use Mouse::Util::TypeConstraints;
+
+ coerce 'Headers' =>
+ from 'ArrayRef' => via {
+ Request::Headers->new(%{ $_ });
+ },
+ ;
+};
+ok !$@;
+
+{
+ package Request;
+ use Mouse;
+
+ has headers => (
+ is => 'rw',
+ isa => 'Headers',
+ coerce => 1,
+ );
+}
+
+my $req = Request->new(headers => { foo => 'bar' });
+isa_ok($req->headers, 'Response::Headers');
+is($req->headers->foo, 'bar');
+$req->headers({foo => 'yay'});
+isa_ok($req->headers, 'Response::Headers');
+is($req->headers->foo, 'yay');
+
+my $res = Response->new(headers => { foo => 'bar' });
+isa_ok($res->headers, 'Response::Headers');
+is($res->headers->foo, 'bar');
+$res->headers({foo => 'yay'});
+isa_ok($res->headers, 'Response::Headers');
+is($res->headers->foo, 'yay');
+