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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
       arguments as
	  supplied  to emplace,	forwarded via std::forward<Args>(args).... The
       element may be
	  constructed even if there already is an element with the key in  the
       container, in
	  which	 case  the newly constructed element will be destroyed immedi-
       ately.

	  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
       element 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  ef-
       fect (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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