alt Hacker NewsI'm fairly out of touch with Rust. I think generics and lifetimes are also separate in the sense that only the generics get monomorphised, while lifetimes don't. I.e., you get distinct structs Foo<u32> and Foo<i32>, depending on the (type) argument with which Foo was instantiated (just like it is in C++), but only one Bar<'a> no matter what (lifetime) argument it was "instantiated" with.
You're slightly incorrect. Lifetimes do get "monomorphized" in the sense that you can have multiple concrete lifetimes be filled in for a given lifetime parameter (that's why they're called parameters) but also, lifetimes are fully erased far before you get to codegen monomorphization, which is what happens with generics.