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std::set::emplace(3)	       C++ Standard Libary	    std::set::emplace(3)

NAME
     std::set::emplace - std::set::emplace

Synopsis
	template< class... Args >			      (since C++11)
	std::pair<iterator, bool> emplace( Args&&... args );

	Inserts  a  new element into the container constructed in-place with the
     given args,
	if there is no element with the key in the container.

	The constructor of the new element is called with exactly the same argu-
     ments as
	supplied to emplace, forwarded via std::forward<Args>(args).... The ele-
     ment may be
	constructed even if there already is an element with the key in the con-
     tainer, in
	which case the newly constructed element will be destroyed immediately.

	Careful use of emplace allows the new element to  be  constructed  while
     avoiding
	unnecessary copy or move operations.

	No iterators or references are invalidated.

Parameters
	args - arguments to forward to the constructor of the element

Return value
	A pair consisting of an iterator to the inserted element (or to the ele-
     ment that
	prevented the insertion) and a bool value set to true if and only if the
     insertion
	took place.

Exceptions
	If  an	exception  is thrown for any reason, this function has no effect
     (strong
	exception safety guarantee).

Complexity
	Logarithmic in the size of the container.

Example
     // Run this code

      #include <chrono>
      #include <cstddef>
      #include <functional>
      #include <iomanip>
      #include <iostream>
      #include <string>
      #include <set>

      class Dew
      {
      private:
	  int a, b, c;

      public:
	  Dew(int _a, int _b, int _c)
	      : a(_a), b(_b), c(_c)
	  {}

	  bool operator<(const Dew& other) const
	  {
	      return (a < other.a) ||
		     (a == other.a && b < other.b) ||
		     (a == other.a && b == other.b && c < other.c);
	  }
      };

      constexpr int nof_operations{101};

      std::size_t set_emplace()
      {
	  std::set<Dew> set;
	  for (int i = 0; i < nof_operations; ++i)
	      for (int j = 0; j < nof_operations; ++j)
		  for (int k = 0; k < nof_operations; ++k)
		      set.emplace(i, j, k);

	  return set.size();
      }

      std::size_t set_insert()
      {
	  std::set<Dew> set;
	  for (int i = 0; i < nof_operations; ++i)
	      for (int j = 0; j < nof_operations; ++j)
		  for (int k = 0; k < nof_operations; ++k)
		      set.insert(Dew(i, j, k));

	  return set.size();
      }

      void time_it(std::function<int()> set_test, std::string what = "")
      {
	  const auto start = std::chrono::system_clock::now();
	  const auto the_size = set_test();
	  const auto stop = std::chrono::system_clock::now();
	  const std::chrono::duration<double, std::milli> time = stop - start;
	  if (!what.empty() && the_size)
	      std::cout << std::fixed << std::setprecision(2)
			<< time << " for " << what << '\n';
      }

      int main()
      {
	  time_it(set_insert, "cache warming...");
	  time_it(set_insert, "insert");
	  time_it(set_insert, "insert");
	  time_it(set_emplace, "emplace");
	  time_it(set_emplace, "emplace");
      }

Possible output:
      630.58ms for cache warming...
      577.16ms for insert
      560.84ms for insert
      547.10ms for emplace
      549.44ms for emplace

See also
	emplace_hint constructs elements in-place using a hint
	(C++11)      (public member function)
		     inserts elements
	insert	     or nodes
		     (since C++17)
		     (public member function)

http://cppreference.com 	   2024.06.10		    std::set::emplace(3)
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