Is it possible to create an attribute that can only be set in the constructor in Moose?

Question

Is it possible to create an attribute that can only be set in the constructor in Moose? I’d like to do something like this:

my $foo = new Foo(file => 'foo.txt');
my $bar = new Foo(string => $str);
$foo->file('baz.txt'); # dies

I know I can create an attribute that can not be set in constructor, but the complementary case seems to be missing.

Answer 1

Isn't that just a read-only attribute? If I write

package Foo;
use Moose;

has 'file' => (is => 'ro', isa => 'Str');
has 'string' => (is => 'rw', isa => 'Str');

1;

then your code dies with

Cannot assign a value to a read-only accessor