std::make_any(3) - FreeBSD Ports 15.1.quarterly Manual Pages

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

NAME
     std::make_any - std::make_any

Synopsis
	Defined in header <any>
	template<  class  T,  class... Args >				     (1)
     (since C++17)
	std::any make_any( Args&&... args );
	template< class T, class U, class...  Args  >			     (2)
     (since C++17)
	std::any make_any( std::initializer_list<U> il, Args&&... args );

	Constructs  an	any  object  containing an object of type T, passing the
     provided
	arguments to T's constructor.

	1) Equivalent to return std::any(std::in_place_type<T>,
	std::forward<Args>(args)...);
	2) Equivalent to return std::any(std::in_place_type<T>, il,
	std::forward<Args>(args)...);

Example
     // Run this code

      #include <any>
      #include <complex>
      #include <functional>
      #include <iostream>
      #include <string>

      int main()
      {
	  auto a0 = std::make_any<std::string>("Hello, std::any!\n");
	  auto a1 = std::make_any<std::complex<double>>(0.1, 2.3);

	  std::cout << std::any_cast<std::string&>(a0);
	  std::cout << std::any_cast<std::complex<double>&>(a1) << '\n';

	  using lambda = std::function<void(void)>;

	  // Put a lambda into std::any. Attempt #1 (failed).
	  std::any a2 = [] { std::cout << "Lambda #1.\n"; };
	  std::cout << "a2.type() = \"" << a2.type().name() << "\"\n";

	  // any_cast casts to <void(void)> but actual type is not
	  // a std::function..., but ~ main::{lambda()#1}, and it is
	  // unique for each lambda. So, this throws...
	  try
	  {
	      std::any_cast<lambda>(a2)();
	  }
	  catch (std::bad_any_cast const& ex)
	  {
	      std::cout << ex.what() << '\n';
	  }

	  // Put a lambda into std::any. Attempt #2 (successful).
	  auto a3 = std::make_any<lambda>([] { std::cout << "Lambda #2.\n"; });
	  std::cout << "a3.type() = \"" << a3.type().name() << "\"\n";
	  std::any_cast<lambda>(a3)();
      }

Possible output:
      Hello, std::any!
      (0.1,2.3)
      a2.type() = "Z4mainEUlvE_"
      bad any_cast
      a3.type() = "St8functionIFvvEE"
      Lambda #2.

See also
	constructor   constructs an any object
		      (public member function)
	any_cast      type-safe access to the contained object
	(C++17)       (function template)

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

NAME | Synopsis | Example | Possible output: | See also

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