Moo Archives

Exploring Type::Tiny Part 7: Creating a Type Library with Type::Library

Type::Tiny is probably best known as a way of having Moose-like type constraints in Moo, but it can be used for so much more. This is the seventh in a series of posts showing other things you can use Type::Tiny for. This article along with the earlier ones in the series can be found on my blog and in the Cool Uses for Perl section of PerlMonks.

For small projects, the type constraints in Types::Standard and other CPAN type libraries are probably enough to satisfy your needs. You can do things like:

   use Types::Common::Numeric qw(PositiveInt);
   has user_id => (
      is   => 'ro',
      isa  => PositiveInt,

However for larger apps, say you need to check user identity numbers in an handful of places throughout your code and you use PositiveInt everywhere, then if you ever feel the need to change the constraint for them, you'll need to hunt through your code to look for every use of PositiveInt, make sure it's not being used for some other reason (like to check an age or a counter), and update it.

So it is helpful to make your own application-specific type library. You can define your own UserId type constraint, and use that everywhere. If the format of your identifiers ever changes, you only need to change the definition of the type constraint.

About Toby Inkster

user-pic I'm tobyink on CPAN, IRC and PerlMonks.