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

NAME
       std::empty - std::empty

Synopsis
	  Defined in header <array>
	  Defined in header <deque>
	  Defined in header <flat_map>
	  Defined in header <flat_set>
	  Defined in header <forward_list>
	  Defined in header <iterator>
	  Defined in header <list>
	  Defined in header <map>
	  Defined in header <regex>
	  Defined in header <set>
	  Defined in header <span>
	  Defined in header <string>
	  Defined in header <string_view>
	  Defined in header <unordered_map>
	  Defined in header <unordered_set>
	  Defined in header <vector>
	  template< class C >					       (since
	  constexpr auto empty(	const C& c ) ->			       C++17)
	  decltype(c.empty());					       (until
								       C++20)
	  template< class C >					       (since
	  [[nodiscard]]	constexpr auto empty( const C& c ) ->	       C++20)
	  decltype(c.empty());
	  template<	   class	T,	  std::size_t	     N	     >
       (since
	  constexpr	bool	 empty(	    const     T	    (&array)[N]	     )
       C++17)
	  noexcept;
       (until
							       (1)
       C++20)
	  template<	   class	T,	  std::size_t	     N	     >
       (since
	  [[nodiscard]]	     constexpr	    bool      empty(	  const	     T
       C++20)
	  (&array)[N] )	noexcept;				   (2)
	  template<		     class		   E		     >
       (since
	  constexpr    bool    empty(	 std::initializer_list<E>     il     )
       C++17)
	  noexcept;
       (until
								       (3)
       C++20)
	  template<		     class		   E		     >
       (since
	  [[nodiscard]]		   constexpr		bool		empty(
       C++20)
	  std::initializer_list<E> il )	noexcept;

	  Returns whether the given range is empty.

	  1) Returns c.empty().
	  2) Returns false.
	  3) Returns il.size() == 0.

Parameters
	  c	- a container or view with an empty member function
	  array	- an array of arbitrary	type
	  il	- an std::initializer_list

Return value
	  1) c.empty()
	  2) false
	  3) il.size() == 0

Exceptions
	  1) May throw implementation-defined exceptions.

Notes
	  The  overload	for std::initializer_list is necessary because it does
       not have	a
	  member function empty.

		   Feature-test	      macro		    Value	   Std
       Feature
	  __cpp_lib_nonmember_container_access	201411L	 (C++17)  std::size(),
       std::data(), and
							       std::empty()

Possible implementation
First version
	  template<class C>
	  [[nodiscard]]	  constexpr   auto   empty(const   C&	c)   ->	   de-
       cltype(c.empty())
	  {
	      return c.empty();
	  }

Second version
	  template<class T, std::size_t	N>
	  [[nodiscard]]	constexpr bool empty(const T (&array)[N]) noexcept
	  {
	      return false;
	  }
				       Third version
	  template<class E>
	  [[nodiscard]]	  constexpr  bool  empty(std::initializer_list<E>  il)
       noexcept
	  {
	      return il.size() == 0;
	  }

Example
       // Run this code

	#include <iostream>
	#include <vector>

	template<class T>
	void print(const T& container)
	{
	    if (std::empty(container))
		std::cout << "Empty\n";
	    else
	    {
		std::cout << "Elements:";
		for (const auto& element : container)
		    std::cout << ' ' <<	element;
		std::cout << '\n';
	    }
	}

	int main()
	{
	    std::vector<int> c = {1, 2,	3};
	    print(c);
	    c.clear();
	    print(c);

	    int	array[]	= {4, 5, 6};
	    print(array);

	    auto il = {7, 8, 9};
	    print(il);
	}

Output:
	Elements: 1 2 3
	Empty
	Elements: 4 5 6
	Elements: 7 8 9

See also
	  ranges::empty	checks whether a range is empty
	  (C++20)	(customization point object)

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

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