Forwarding references, also known as universal references, are a powerful feature in C++ introduced with the C++11 standard. They allow for perfect forwarding of arguments, enabling generic programming and avoiding unnecessary copies or moves.

What Are Forwarding References?

A forwarding reference is a reference that can bind to both lvalue and rvalue expressions. It is declared using the auto&& syntax. The name “forwarding reference” arises from their ability to forward arguments to other functions.

When to Use Forwarding References?

Forwarding references are most commonly used in template functions or classes where the exact type of the arguments can vary. By using forwarding references, you can write code that accepts arguments of any type and efficiently pass them on to other functions.

How Forwarding References Work?

When a forwarding reference is passed an lvalue argument, it deduces the type as an lvalue reference. On the other hand, if it is passed an rvalue argument, it deduces the type as an rvalue reference. This allows for perfect forwarding, ensuring the argument is passed along as-is without unnecessary copies or moves.

Example Code - Forwarding References in Function Templates

template<typename T>
void forwardArguments(T&& arg)
{
    // Process arg here
    // ...

    // Forward the argument to another function
    otherFunction(std::forward<T>(arg));
}

In this example, arg is a forwarding reference as it is declared using the auto&& syntax. The std::forward function is used to pass arg to another function while preserving its value category (lvalue or rvalue).

Conclusion

Forwarding references provide a powerful way to write generic code in C++, allowing for perfect forwarding of arguments. By using forwarding references, you can create more efficient and flexible code that can handle a wide range of argument types. Usage of forwarding references in C++ templates can greatly improve code reusability and performance.

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