CODEWITHSUNDEEP
c++templatesc++17variadic-templates
Filipp
Filipp

Reputation: 2040

Why do structured bindings not support variadics?

C++17 adds structured bindings:

tuple<int, int, int> make_tuple();
int test() {
    auto [a, b, c] = make_tuple();
    return a | b | c;
}

My immediate instinct was to try using them as parameter packs.

template <size_t N>
auto make_tuple();  // returns tuple with N ints
template <size_t N>
int test() {
    auto [...values] = make_tuple<N>();
    return (0 | ... | values);
}

Alas, I cannot do this. Why did the committee exclude such functionality? It feels inconsistent now that lambda captures can contain parameter packs.

I know the committee is full of intelligent creative people, and an idea like mine must have come up and been rejected for good reason. What is that reason?

Upvotes: 5

Views: 310

Answers (1)

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385385

It is the nature of a developing language that features be added over time.

Just because something is not in the language yet, does not mean that the committee already rejected it outright. It does not mean that they "excluded" it. It could just be that it was overlooked, or just hadn't been seriously considered yet. Remember, std::make_unique wasn't available until C++14.

In this particular case, it's a feature that has been proposed, quite recently, as P1061. You'll note from the revision history section that the committee "reviewed it favorably and thought this was a good investment of our time". So I guess you're in luck. :)

Upvotes: 9

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