result of substr fails 'Str' validation

[jira]

Hello,

consider the code fragment below. Why does it fail on 
'$person->name(substr 'John', 0, 255)' ?
"Attribute (name) does not pass the type constraint because: Validation 
failed for 'Str' failed with value John"


Thank you,
Jiri


-----------------------------------------------------

package Person;

use Moose;


has name => (
  is  => 'rw',
  isa => 'Str',
);

1;

package main;

my $person = Person->new;
$person->name('John');

print 'person name is: ', $person->name, "\n";

$person->name(substr 'John', 0, 255);

print 'person name is: ', $person->name, "\n";