wait_for_all waits on futures on implicit specific order.

[ivg@…]

Either, the order in which futures must happen must be specified explicitly in the documentation, or, may be, a wait_for_all can be implemented via wait_for_any. For example, a range based wait_for_all:

    template <typename FutureIterator>
    void wait_for_all(FutureIterator first, FutureIterator last) {
        for (;first != last; ++first) 
            std::iter_swap(first, boost::wait_for_any(first, last));
    }

[Steven Watanabe]

Why do you care what order it waits in?

[Anthony Williams]

The function is documented to not return until all futures are ready. This is true.

The documentation doesn't specify what order the futures are waited for, so if your code relies on a specific order then your code is broken.