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)