what is the preferred way to expose custom STL-style iteration?

Question

(also see Is there a good way not to hand-write all twelve required Container functions for a custom type in C++? )

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For a class such as

namespa         


        

Answer 1

I'll take option C.

The main problem here is that std::begin() doesn't actually work for finding non-member begin() with ADL. So the real solution is to write your own that does:

namespace details {
    using std::begin;

    template 
    constexpr auto adl_begin(C& c) noexcept(noexcept(begin(c)))
        -> decltype(begin(c))
    {
        return begin(c);
    }
}

using details::adl_begin;

Now, it doesn't matter if you write your begin() as a member or non-member function, just use adl_begin(x) everywhere and it'll just work. As well as for both the standard containers and raw arrays. This conveniently side-steps the member vs. non-member discussion.

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And yes, you should have const and non-const overloads of begin() and friends, if you want to expose const and non-const access.