Question

I have a variable i of type std::size_t and a tuple of type std::tuple. I want to get the i-th element of the tuple. I tried this:

// bindings... is of type const T&...
auto bindings_tuple = std::make_tuple(bindings...);
auto binding = std::tuple_element<i, const T&...>(bindings_tuple);

But I get this compile error saying that the first template argument must be an integral constant expression:

error: non-type template argument of type ‘std::size_t‘ (aka ‘unsigned long‘) is not an integral constant expression

Is it possible to get the i-th element of a tuple, and how to do that?

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_{^{I would like to do this without using boost, if possible.}}

Answer 1

You cannot. That’s not what a tuple is for. If you need dynamic access to an element, use std::array<T,N>, which is almost identical to std::tuple<T,...,T> but gives you the dynamic [i]-operator; or even a fully dynamic container like std::vector<T>.