[wyager]

A couple reasons that wouldn't work well (there may be more, I haven't thought about this much):

1. Using an interface would nuke your performance. Data structures where every data structure operation requires one or more vtable lookups on items in the structure can really hurt your time and space performance. To get good performance, you need true type-level generics so the compiler can specialize at compile time.

2. Anyone could put anything that followed the interface in the data structure, even if it was of the wrong type. To get any form of static type safety, you'd still have to define a wrapper type and a bunch of functions for every type you'd want to put in the data structure. You could save a bit of work by re-using your (slow) code you wrote generically using interfaces.