tie a variable to a type constraint


Type::Tie is a response to this sort of problem...

   use strict;
   use warnings;
      package Local::Testing;
      use Moose;
      has numbers => ( is => "ro", isa => "ArrayRef[Num]" );
   # Nice list of numbers.
   my @N = ( 1, 2, 3, 3.14159 );
   # Create an object with a reference to that list.
   my $object = Local::Testing->new(numbers => \@N);
   # Everything OK so far...
   # Now watch this!
   push @N, "Monkey!";
   print $object->dump;
   # Houston, we have a problem!

Just declare @N like this:

   use Type::Tie;
   use Types::Standard qw( Num );
   ttie my @N, Num, ( 1, 2, 3, 3.14159 );

Now any attempt to add a non-numeric value to @N will die.


This module exports a single function: ttie. ttie ties a variable to a type constraint, ensuring that whatever values stored in the variable will conform to the type constraint. If the type constraint has coercions, these will be used if necessary to ensure values assigned to the variable conform.

   use Type::Tie;
   use Types::Standard qw( Int Num );
   ttie my $count, Int->plus_coercions(Num, 'int $_'), 0;
   $count++;            # ok
   $count = 2;          # ok
   $count = 3.14159;    # ok, coerced to 3
   $count = "Monkey!";  # dies

While the examples in documentation (and the test suite) show type constraints from Types::Standard, but any type constraint objects supporting the Type::API interfaces should work. This includes:

About Cloning with Storage::dclone (and Clone::clone)

Cloning variables with Storage::dclone works, but cloning with Clone::clone is not possible. See Bug #127576 for Type-Tie: Doesn't work with Clone::clone


Please report any bugs to http://rt.cpan.org/Dist/Display.html?Queue=Type-Tie.


IRC: support is available through in the #moops channel on irc.perl.org.

See Also

Type::API, Type::Utils, Moose::Manual::Types, MooseX::Lexical::Types.

External Module
This module is not included in the base Type::Tiny distribution. It needs installing from the CPAN separately.