c++ - Initialize an std::array of tuples with curly braces

Question

This probably has a very simple answer, but I really can't figure it out. Why do I get errors for doing this? What's the correct way to initialize something like this?

std::array<std::tuple<int, std::string>, 3> tuples{
    {3, "a"},
    {7, "b"},
    {2, "c"}
};

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On MSVC 2015, I get the following errors:

No suitable constructor exists to convert from "int" to "std::tuple<int, std::string>"
No suitable constructor exists to convert from "const char[2]" to "std::tuple<int, std::string>"

Answer 1

This is an outstanding issue with tuple. See, its constructor in C++11/14 is explicit. And therefore, it cannot participate in copy-list-initialization, which is what the inner braced-init-lists do (the outer ones are direct-list-initialization).

The idea was to prevent you from being able to bypass a class's explicit constructors through tuple. But, in C++17, this will be changed: if all of the tuple's types themselves are implicitly convertible from the respective given type, then so too will that constructor of tuple.

For your specific use case, you could use std::pair. Its constructor is never explicit.