Subtyping in Rust and Clarke’s Third Law

“Any sufficiently advanced technology is indistinguishable from magic.” – Arthur C Clarke

This is a talk about magic. In particular: Rust has subtyping, but it may not be in the place where you thought it was. My primary goal is to explain that metaphorical sleight-of-hand, in two parts. My secondary goal is to convey that most of the time you need not think about subtyping, except when doing particularly hairy data structure development where questions arise around “variance.”