Swift takes this approach: monomorphisation is an implementation detail/optimisation. In languages like Rust and Swift where values don't have a uniform repres

Swift takes this approach: monomorphisation is an implementation detail/optimisation. In languages like Rust and Swift where values don't have a uniform representation (that is, not always a pointer), this takes a lot of infastructure, and a lot of performance/optimiser work to get reasonable performance for common code: the Swift compiler has quite a bit of code devoted to making generically-types values behave mostly like statically-typed ones, with minimal performance cliffs. Rust's approach is that this sort of vtable-/dictionary-passing has to be done explicitly (with a trait object), and such values have restrictions.