Elsewhere, you posted http://article.gmane.org/gmane.comp.lang.perl.moose/1697

which has two possible values, None, meaning no value, and Some(`a) meaning a value of the type `a

That sounds like a union, so I tried it. Coercion works! ...but constraints don't?! Am I missing something?

Simple demonstration: 

$ perl -Moose -e'has a=>(is=>"rw",isa=>"Undef",coerce=>1); __PACKAGE__
+->new(a=>"abc")'
Attribute (a) does not pass the type constraint because: Validation fa
+iled for 'Undef' failed with value abc at [snip backtrace]

$ perl -Moose -e'has a=>(is=>"rw",isa=>"Undef|Undef",coerce=>1); __PAC
+KAGE__->new(a=>"abc")'

$ perl -Moose -e'has a=>(is=>"rw",isa=>"Undef|Undef",coerce=>0); __PAC
+KAGE__->new(a=>"abc")'
Attribute (a) does not pass the type constraint because: Validation fa
+iled for 'Undef|Undef' failed with value abc at [snip backtrace]

[download]

Full demonstration: 

BEGIN {
   package Class;

   use strict;
   use warnings;

   use Moose;

   has val => (
      is       => 'rw',
      isa      => 'Num',
      required => 1,
   );


   use Moose::Util::TypeConstraints;

   coerce __PACKAGE__
      => from 'Num'
         => via { __PACKAGE__->new(val => $_) };
 }


BEGIN {
   package Container;

   use strict;
   use warnings;

   use Moose;

   has always => (
      is      => 'rw',
      isa     => 'Class',
      coerce  => 1,
      default => sub { Class->new(val => 0) },
   );

   has union => (
      is      => 'rw',
      isa     => 'Undef|Class',
      coerce  => 1,
      default => undef,
   );
}

use strict;
use warnings;

use Test::More tests => 30;

use Scalar::Util qw( blessed );

sub ta { $_[0] && blessed($_[0]->always) && blessed($_[0]->always) eq 
+'Class' }
sub tu { $_[0] && ( !$_[0]->union || blessed($_[0]->union) && blessed(
+$_[0]->union) eq 'Class' ) }

my $always_fail = qr/^Attribute \(always\) does not pass the type cons
+traint/;
my $union_fail  = qr/^Attribute \(union\) does not pass the type const
+raint/;

my $o = Class->new(val => 123);
my $c;

$c = eval { Container->new() };                 is($@, '');           
+   ok(ta($c));
$c = eval { Container->new(always => $o) };     is($@, '');           
+   ok(ta($c));
$c = eval { Container->new(always => 123) };    is($@, '');           
+   ok(ta($c));
$c = eval { Container->new(always => "abc") };  like($@, $always_fail)
+;  ok(!$c);

$c = eval { Container->new(union => undef) };   is($@, '');           
+   ok(tu($c));
$c = eval { Container->new(union => $o) };      is($@, '');           
+   ok(tu($c));
$c = eval { Container->new(union => 123) };     is($@, '');           
+   ok(tu($c));
$c = eval { Container->new(union => "abc") };   like($@, $union_fail);
+   ok(!$c);

$c = Container->new();

eval { $c->always($o) };     is($@, '');              ok(tu($c));
eval { $c->always(123) };    is($@, '');              ok(tu($c));
eval { $c->always("abc") };  like($@, $always_fail);  ok(tu($c));

eval { $c->union(undef) };   is($@, '');              ok(tu($c));
eval { $c->union($o) };      is($@, '');              ok(tu($c));
eval { $c->union(123) };     is($@, '');              ok(tu($c));
eval { $c->union("abc") };   like($@, $union_fail);   ok(tu($c));

[download]
$ perl a.pl
1..30
ok 1
ok 2
ok 3
ok 4
ok 5
ok 6
ok 7
ok 8
ok 9
ok 10
ok 11
ok 12
ok 13
ok 14
not ok 15
#   Failed test at a.pl line 71.
#                   ''
#     doesn't match '(?-xism:^Attribute \(union\) does not pass the ty
+pe constraint)'
not ok 16
#   Failed test at a.pl line 71.
ok 17
ok 18
ok 19
ok 20
ok 21
ok 22
ok 23
ok 24
ok 25
ok 26
ok 27
ok 28
not ok 29
#   Failed test at a.pl line 82.
#                   ''
#     doesn't match '(?-xism:^Attribute \(union\) does not pass the ty
+pe constraint)'
ok 30
# Looks like you failed 3 tests of 30.

[download]

In reply to Re^2: Moose type question by ikegami
in thread Moose type question by Sue D. Nymme

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.