Constant attributes

I wanted a constant attribute, i.e., one that is read-only and not settable
at construction time. I found a solution by making it a class attribute
with MooseX::ClassAttribute, setting its 'is' property to 'ro', and
providing a default value.

It seems a bit of a roundabout solution, so I'm wondering whether there is a
better way to go about constant attributes. Any suggestions?

Bernardo