Moose Archives

Exploring Type::Tiny Part 2: Using Type::Tiny with Moose

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 second in a series of posts showing other things you can use Type::Tiny for. You can refer back to part 1.

Type::Tiny is often used in Moo classes and roles as a drop-in replacement for Moose's built-in type system. But the original reason I wrote it was as a response to the growing number of MooseX::Types and MouseX::Types modules on CPAN. I thought "wouldn't it be good if you could write a type library once, and use it for Moose, Mouse, and maybe even Moo?" In the very early version, you needed to import types like this:

   use Type::Standard -moose, qw(Int);
   use Type::Standard -mouse, qw(Int);
   use Type::Standard -moo,   qw(Int);

Specifying which object system you were using allowed the type library to export different blessed type constraint objects for different object frameworks. Eventually this need was eliminated by having Type::Tiny's objects better mock the Moose and Mouse native APIs, so the frameworks didn't even notice you weren't using their built-in type constraints.

(While no longer documented, the -moose, etc import flags still work in all Type::Library-based type libraries.)

Anyway, so now you know Type::Tiny types can work with Moose, what are the reasons to use them over Moose's built-in type constraints?

What is a Bool?

Perl allows pretty much any value to be evaluated in a boolean context:

if ($something) {
   ...
}

No matter what $something is, it will safely evaluate to either true or false. (With the exceptions of a few edge cases like blessed objects which are overloaded to throw an error when evaluated as booleans.)

So when a Moose class does something like this, what does it mean?

has something => (
   is  => 'ro',
   isa => 'Bool',
);

Perils of Plugins

Plugin-based architectures can be a bad idea.

Not always. In user-facing applications, where the list of installed and enabled plugins is clear, then plugins are often a good thing. This article is concerned not with end-user facing applications, but with libraries. Libraries that allow their functionality to be extended through plugins. In particular, libraries that automatically detect and load all installed plugins.

Plugins aren't always obviously plugins. In this article, I'm defining a plugin as a software module that adds additional functionality or modifies the external…

About Toby Inkster

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