[rripken]

Is this in reference to the type classes as seen in Haskell or something else? I want to reach enlightenment but I'm stuck in Java for the time being.

[jdmichal]

Yes, as in Haskell type classes. Or Rust traits. Basically, anything that acts like an interface (defines a contract) but allows external definition. So you're not stuck wrapping your Integer in a ShowableInteger just to have an Integer that implements the Show interface.