Rust's generics are entirely type-based, not syntax-based. They must declare all the traits (concepts) they need. The type system has restrictions that prevent violating ODR. It's very reliable, but some use-cases that would be basic in C++ (numeric code) can be tedious to define.

Generic code is stored in libraries as MIR, which is half way between AST and LLVM IR. It's still monomorphic and slow to optimize, but at least doesn't pay reparsing cost.

How does it handle an implementation of a trait being in scope in one compilation unit and out of scope in another? That's the wicked problem.