C++ has extensive type inference now (C++20):

    #include <string>

    auto func(auto x, auto y) -> auto {
        return x + y;
    }

    auto main() -> int {
        auto i = func(1, 2);
        auto s = func(std::string("a"), std::string("b"));
    }

`int` is required as a return type from `main`, but everything else is inferred. This works because `func` becomes a template function where each parameter type is a separate template type, so you get compile-time duck typing. It also works with concepts (e.g. `std::integral auto x`).

It's quite neat, but I don't think anyone actually writes code this way, except for lambdas.