As usual C++ choose to something much weirder and more dangerous. Instead of inference C++ can deduce types, in some cases there's no way to write a type's name so you have to deduce types, and they can be deduced at the edges of functions however unlike inference it's not an error to have ambiguity, in some cases deduction may choose one of the possibilities that it liked better even if that's astonishing for you.

Because Rust's functions must tell you their types explicitly, and because some types can't be named specifically, the result is that in Rust you have to write these functions polymorphically, even if in practice there's only one possibility. In C++ you can write the non-polymorphic function, despite not being able to say the name of the type. How do you document that? It's OK, C++ doesn't require you to provide even halfway usable documentation.

I think PureScript has the best compromise here, top-level type signatures are not enforced but if you don't include one you'll get a warning with the inferred signature. On the one hand, this is very helpful because sometimes I have a grasp for what expression I want to use, but am not sure about its type, so I simply comment out the desired signature and let the compiler tell me which direction I'm moving in, i.e. what's the type of what I just wrote. On the other hand, it being a warning also basically ensures nobody writes their top-level functions without the type signatures. Really the best of the two worlds. I think simply disallowing top-level functions without type signatures would hurt my workflow a lot.