std::forward_as_tuple(3)

💖 std::forward_as_tuple(3) 💖

okay bestie, welcome to the std::forward_as_tuple(3) page from the C++ Standard Libary manual 💖 yes, that's the manual name folded in near the top, we're doing this cute and correct.

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🌸 NAME 🌸

std::forward_as_tuple — std::forward_as_tuple.

That's literally the NAME line, she's minimal and iconic 💅

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✨ Synopsis ✨

Defined in header <tuple> 🎀

template< class... Types >                                   (since C++11)
tuple<Types&&...> forward_as_tuple( Types&&... args )
(constexpr since C++14)
noexcept;

Bestie, what this does: it constructs a tuple of references to the arguments in args, and that tuple is suitable for forwarding as an argument to a function. The tuple has rvalue reference data members when rvalues are used as arguments, and otherwise it has lvalue reference data members. No cap ✨

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🎀 Parameters 🎀

• args — zero or more arguments to construct the tuple from 🫶

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🌸 Return value 🌸

A std::tuple object created as if by:

std::tuple<Types&&...>(std::forward<Types>(args)...)

That's the whole return-value tea ☕✨

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🦋 Notes 🦋

If the arguments are temporaries, forward_as_tuple does not extend their lifetime 😭 — they have to be used before the end of the full expression. Fr fr, do not let them dangle.

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💅 Example 💅

// Run this code

#include <iostream>
#include <map>
#include <tuple>
#include <string>

int main()
{
    std::map<int, std::string> m;

    m.emplace(std::piecewise_construct,
              std::forward_as_tuple(10),
              std::forward_as_tuple(20, 'a'));
    std::cout << "m[10] = " << m[10] << '\n';

    // The following is an error: it produces a
    // std::tuple<int&&, char&&> holding two dangling references.
    //
    // auto t = std::forward_as_tuple(20, 'a');
    // m.emplace(std::piecewise_construct, std::forward_as_tuple(10),
       t);
}

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🍓 Output 🍓

m[10] = aaaaaaaaaaaaaaaaaaaa

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🌈 See also 🌈

• make_tuple — creates a tuple object of the type defined by the argument types. (C++11) (function template)
• tie — creates a tuple of lvalue references or unpacks a tuple into individual objects. (C++11) (function template)
• tuple_cat — creates a tuple by concatenating any number of tuples. (C++11) (function template)
• apply — calls a function with a tuple of arguments. (C++17) (function template)

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That's the whole page, bestie 🫶 — source: http://cppreference.com, version date: 2024.06.10, page: std::forward_as_tuple(3). Byeee 💖✨