Yes, exactly. I can see why people say that Go already had a sort of built-in generics feature. However, I think the same could be said about any language that

Yes, exactly. I can see why people say that Go already had a sort of built-in generics feature. However, I think the same could be said about any language that allows you to define arrays with different element types (e.g. C). In common parlance, a language has generics iff it permits you to explicitly abstract over types. I wish it had occurred to me earlier that C vs. C++ is a good test case here. If generics really led to huge performance improvements in typical application-level code, we'd expect C++ programs to run much faster than C programs. Typically, they don't. Of course there are exceptions, such as code that benefits from libraries like uBLAS. (I'm aware that you can fake generics in C using macros, but there are also comparable code generation tools for Go.)