[masklinn]

> You're getting into pedantics about specific languages

No, I'm using terms which clearly express what I'm talking about, and referring to actual historical experience with these concerns.

> Implement a function that takes three strings without 3! permutations of that function either explicitly or implicitly created.

In the overwhelming majority of cases this is a nonsensical requirement, if the function can take 3 borrowed strings you just implement a single function which takes 3 borrowed strings.

In the (rare) situation where optimising for maybe-owned makes sense, you use a wrapper type over "owned or borrowed". Which still needs no "interface or inheritance".