std::plus<void> - cppreference.com

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# std::plus<void>

From cppreference.com
< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
template<> class plus<void>; |  | (since C++14)

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

### [edit] Member types

Member type | Definition
`is_transparent` | /* unspecified */

### [edit] Member functions

operator() | returns the sum of two arguments (public member function) [edit]

# std::plus<>::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

lhs, rhs | - | values to sum

### Return value

The result of lhs + rhs.

### [edit] Notes

The member type `is_transparent` indicates to the caller that this function object is a transparent function object: it accepts arguments of arbitrary types and uses perfect forwarding, which avoids unnecessary copying and conversion when the function object is used in heterogeneous context, or with rvalue arguments. In particular, template functions such as std::set::find and std::set::lower_bound make use of this member type on their `Compare` types.

### [edit] Example

Run this code

    #include <functional>
    #include <iostream>

    int main()
    {
        std::string a = "Hello ";
        const char* b = "world";
        std::cout << std::plus<>{}(a, b) << '\n';
    }

Output:

    Hello world

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