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

NAME
       std::any::emplace - std::any::emplace

Synopsis
	  template<	  class	     ValueType,	     class...	   Args	     >
       (1) (since C++17)
	  std::decay_t<ValueType>& emplace( Args&&... args );
	  template< class ValueType, class U, class... Args >
	  std::decay_t<ValueType>&   emplace(	std::initializer_list<U>   il,
       (2) (since C++17)
	  Args&&... args );

	  Changes  the contained object	to one of type std::decay_t<ValueType>
       constructed from
	  the arguments.

	  First	destroys the current contained object  (if  any)  by  reset(),
       then:

	  1) constructs	an object of type std::decay_t<ValueType>, direct-non-
       list-initialized
	  from std::forward<Args>(args)..., as the contained object.

	    * This overload participates in overload resolution	only if
	      std::is_constructible_v<std::decay_t<ValueType>, Args...>	and
	      std::is_copy_constructible_v<std::decay_t<ValueType>>  are  both
       true.

	  2) constructs	an object of type std::decay_t<ValueType>, direct-non-
       list-initialized
	  from il, std::forward<Args>(args)...,	as the contained object.

	    * This overload participates in overload resolution	only if
	      std::is_constructible_v<std::decay_t<ValueType>,	 std::initial-
       izer_list<U>&,
	      Args...>	 and  std::is_copy_constructible_v<std::decay_t<Value-
       Type>> are both
	      true.

Template parameters
	  ValueType		  -		 contained value type

Type requirements
	  -
	  std::decay_t<ValueType>  must	 meet  the  requirements  of  CopyCon-
       structible.

Return value
	  A reference to the new contained object.

Exceptions
	  Throws  any  exception thrown	by T's constructor. If an exception is
       thrown, the
	  previously contained object (if any) has been	destroyed,  and	 *this
       does not	contain
	  a value.

Example
       // Run this code

	#include <algorithm>
	#include <any>
	#include <iostream>
	#include <string>
	#include <vector>

	class Star
	{
	    std::string	name;
	    int	id;

	public:
	    Star(std::string name, int id) : name { name }, id { id }
	    {
		std::cout << "Star::Star(string, int)\n";
	    }

	    void print() const
	    {
		std::cout << "Star{ \""	<< name	<< "\" : " << id << " };\n";
	    }
	};

	auto main() -> int
	{
	    std::any celestial;
	    // (1) emplace( Args&&... args );
	    celestial.emplace<Star>("Procyon", 2943);
	    const auto*	star = std::any_cast<Star>(&celestial);
	    star->print();

	    std::any av;
	    // (2) emplace( std::initializer_list<U> il, Args&&... args	);
	    av.emplace<std::vector<char>>({  'C',  '+',	 '+', '1', '7' } /* no
       args */ );
	    std::cout << av.type().name() << '\n';
	    const auto*	va = std::any_cast<std::vector<char>>(&av);
	    std::for_each(va->cbegin(),	 va->cend(),  [](char  const&	c)   {
       std::cout << c; });
	    std::cout << '\n';
	}

Possible output:
	Star::Star(string, int)
	Star{ "Procyon"	: 2943 };
	St6vectorIcSaIcEE
	C++17

See also
	  constructor	constructs an any object
			(public	member function)
	  reset		destroys contained object
			(public	member function)

http://cppreference.com		  2022.07.31		  std::any::emplace(3)

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