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std::tie(3)		      C++ Standard Libary		   std::tie(3)

NAME
       std::tie	- std::tie

Synopsis
	  Defined in header <tuple>
	  template<		  class...		 Types		     >
       (since C++11)
	  std::tuple<Types&...>	   tie(	   Types&...	args	)    noexcept;
       (until C++14)
	  template<		  class...		 Types		     >
       (since C++14)
	  constexpr std::tuple<Types&...> tie( Types&... args )	noexcept;

	  Creates a tuple of lvalue references to its arguments	 or  instances
       of std::ignore.

Parameters
	  args - zero or more lvalue arguments to construct the	tuple from.

Return value
	  A std::tuple object containing lvalue	references.

Possible implementation
	  template <typename...	Args>
	  constexpr // since C++14
	  std::tuple<Args&...> tie(Args&... args) noexcept {
	      return {args...};
	  }

Notes
	  std::tie  may	be used	to unpack a std::pair because std::tuple has a
       converting
	  assignment from pairs:

	bool result;
	std::tie(std::ignore, result) =	set.insert(value);

Example
	  std::tie can be used to introduce lexicographical  comparison	 to  a
       struct or to
	  unpack a tuple:

       // Run this code

	#include <iostream>
	#include <string>
	#include <set>
	#include <tuple>

	struct S {
	    int	n;
	    std::string	s;
	    float d;
	    bool operator<(const S& rhs) const
	    {
		// compares n to rhs.n,
		// then	s to rhs.s,
		// then	d to rhs.d
		return std::tie(n, s, d) < std::tie(rhs.n, rhs.s, rhs.d);
	    }
	};

	int main()
	{
	    std::set<S>	set_of_s; // S is LessThanComparable

	    S value{42,	"Test",	3.14};
	    std::set<S>::iterator iter;
	    bool inserted;

	    // unpacks the return value	of insert into iter and	inserted
	    std::tie(iter, inserted) = set_of_s.insert(value);

	    if (inserted)
		std::cout << "Value was	inserted successfully\n";
	}

Output:
	Value was inserted successfully

See also
	  Structured  binding (C++17) binds the	specified names	to sub-objects
       or tuple
				     elements of the initializer
	  make_tuple		     creates a tuple object of	the  type  de-
       fined by	the
	  (C++11)		     argument types
				     (function template)
	  forward_as_tuple	     creates a tuple of	forwarding references
	  (C++11)		     (function template)
	  tuple_cat		     creates a tuple by	concatenating any num-
       ber of tuples
	  (C++11)		     (function template)
	  ignore		      placeholder  to skip an element when un-
       packing a tuple
	  (C++11)		     using tie
				     (constant)

http://cppreference.com		  2022.07.31			   std::tie(3)

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