[tomkwong]

> you just have to keep in your head all the methods that are expected to exist for a given type.

Technically, you don't need to keep that in your head :-) The general approach is to define generic functions and also write docs about how to extend those functions to satisfy interface requirements.

Perhaps not too surprisingly, many of the Julia community people also want to have some official interface support directly from the language. Before that, several open-source projects were spawned to address that gap e.g. here is a shameless plug about my package:

https://github.com/tk3369/BinaryTraits.jl