Add coerce trait

[schwern]

Add a signature trait to turn on type coercion.

Type coercion is very useful to signatures. For example, you can coerce a path string into a Path::Class object or a URI string into a URI object. Type coercion in Moose is declared as part of the type, but the user of the type must decide to turn it on.

MooseX::Method::Signatures uses "is coerce" or "does coerce". "does" is an unfortunate choice because its normally used to declare a role. "is coerce" is grammatically awkward. "is coerced" might be better. For compatibility purposes with MXMS it may be best to accept both.

[barefootcoder]

What I'd actually like to see is a way to do on-the-fly coercion defintions. In the same way that where allows on-demand subtyping without having to declare a subtype, I think that being able to define your coercion right in the signature would be useful.

Syntax would be open for discussion; I was just thinking of using the same from / via keywords that Moose uses for coercion definitions in the types.

[schwern]

We need a coercion trait regardless. Open your idea as another issue?

[barefootcoder]

Yeah, okay, fair enough.