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

NAME
     std::ignore - std::ignore

Synopsis
	Defined in header <tuple>
	const /*unspecified*/ ignore;		  (since C++11)
						  (until C++17)
	inline constexpr /*unspecified*/ ignore;  (since C++17)

	An  object of unspecified type such that any value can be assigned to it
     with no
	effect. Intended for use with std::tie when unpacking a std::tuple, as a
     placeholder
	for the arguments that are not used.

	While the behavior of std::ignore outside of std::tie  is  not	formally
     specified,
	some  code guides recommend using std::ignore to avoid warnings from un-
     used return
	values of [[nodiscard]] functions.

Possible implementation
	namespace detail {
	struct ignore_t
	{
	    template <typename T>
	    constexpr // required since C++14
	    void operator=(T&&) const noexcept {}
	};
	}
	inline constexpr detail::ignore_t ignore; // 'const' only until C++17

Example
	 1. Demonstrates the use of std::ignore together  with	a  [[nodiscard]]
     function.
	 2.  Unpacks a std::pair<iterator, bool> returned by std::set::insert(),
     but only
	    saves the boolean.

     // Run this code

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

      [[nodiscard]] int dontIgnoreMe()
      {
	  return 42;
      }

      int main()
      {
	  std::ignore = dontIgnoreMe();

	  std::set<std::string> set_of_str;
	  bool inserted = false;
	  std::tie(std::ignore, inserted) = set_of_str.insert("Test");
	  if (inserted)
	      std::cout << "Value was inserted successfully\n";
      }

Output:
      Value was inserted successfully

See also
	tie	creates a tuple of lvalue references or unpacks a tuple into in-
     dividual
	(C++11) objects
		(function template)

http://cppreference.com 	   2024.06.10			  std::ignore(3)
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