Comment by logicchains

>so tired of having to hunt down what functions are going to return, sometimes having to resort to just using it

With highly generic functions, it's often not possible to know what they'll return without knowing what you'll call them with. Especially given that D functions like "map" and "reduce" tend to return special iterator types so that the compiler is able to smarty fuse them where possible. If D had concepts like C++20, you could probably describe them with something looking like:

    template<class R>
    
      concept __SimpleView =                         //     exposition only
        ranges::view<R> && ranges::range<const R> &&
        std::same_as<std::ranges::iterator_t<R>, std::ranges::iterator_t<const R>> &&
        std::same_as<std::ranges::sentinel_t<R>, std::ranges::sentinel_t<const R>>;

But at least for me that doesn't seem like it would be much more helpful than just reading the documentation, which states what the function returns, if not necessarily the type.