How to initialize all tuple elements by the same arguments?

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The clearest way is just to construct each element in the tuple constructor argument list:

template <typename... TElements>
struct Container {
    Container(Foo foo, Bar bar)
        : tuple(TElements{foo, bar}...)
    {}
    std::tuple<TElements...> tuple;
};

This will result in move (or copy) constructing each element of the tuple from its corresponding constructor parameter; if this is unacceptable you could use piecewise construction:

template <typename... TElements>
struct Container {
    Container(Foo foo, Bar bar)
        : tuple(std::piecewise_construct, (sizeof(TElements), std::tie(foo, bar))...)
    {}
    std::tuple<TElements...> tuple;
};

Unfortunately in this case we have to do some kind of gymnastics (here sizeof and a comma operator) to get the variadic list TElements mentioned and ignored.

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