std::plus<void> - cppreference.com

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template<> class plus<void>;		(since C++14)

std::plus<void> is a specialization of std::plus with parameter and return type deduced.

Member types

Member functions

std::plus<void>::operator()

template< class T, class U > constexpr auto operator()( T&& lhs, U&& rhs ) const -> decltype(std::forward<T>(lhs) + std::forward<U>(rhs));

Returns the sum of lhs and rhs.

Parameters

Return value

std::forward<T>(lhs) + std::forward<U>(rhs).

Example

#include <functional>
#include <iostream>

int main()
{
    auto string_plus = std::plus<void>{}; // “void” can be omitted
    std::string a = "Hello ";
    const char* b = "world";
    std::cout << string_plus(a, b) << '\n';
}

Output: