What's the Difference Between Universal References and Forwarding References in C ?

Universal and Forwarding References: A Comprehensive Explanation

In C , programmers often use references to pass data to functions. When defining a function parameter as an rvalue reference (e.g., void f(int && i)), the function argument will be bound to an rvalue reference. Conversely, a template function parameter declared as T && t can be bound to either an rvalue or an lvalue reference.

These two parameter types have sparked discussions, with some referring to the latter as a "universal reference" and others as a "forwarding reference."

Universal Reference vs. Forwarding Reference

The term "universal reference" was originally coined by Scott Meyers to describe the ability of an rvalue reference to a cv-unqualified template parameter to deduce itself as either a value or an lvalue reference. However, C 17 introduced a new term: "forwarding reference."

According to the C standard, a "forwarding reference" is defined as an rvalue reference to a cv-unqualified template parameter. When the function argument is an lvalue, the type "lvalue reference to A" is used for type deduction.

Therefore, universal references and forwarding references are synonymous, and the current preferred term in the C standard is "forwarding reference."

Forwarding References and std::forward()

The function std::forward() forwards its argument to another function or a function object. It is often used to preserve the type of an argument, particularly when the argument is a universal reference. However, using std::forward() is not a requirement for a parameter to be considered a forwarding reference.

Conclusion

Forwarding references provide a flexible way to handle function parameters. They can bind to rvalue or lvalue references, offering convenience and flexibility in code development. Understanding the distinction between forwarding references and universal references is essential for writing efficient and maintainable C code.

The above is the detailed content of What's the Difference Between Universal References and Forwarding References in C ?. For more information, please follow other related articles on the PHP Chinese website!