Why Do Forwarding References and Rvalue References Share the Same Syntax in C ?

Forwarding References and Rvalue References: Shared Syntax Explained

In C , forwarding references and rvalue references hold a special relationship, sharing a similar syntax. This similarity raises the question of whether it causes confusion and whether alternative syntaxes were considered.

Universal References as Forwarding References

Universal references (also known as forwarding references) use the syntax T&&. They differ from rvalue references (T&&) in their ability to bind to both lvalues (references to objects) and rvalues (objects themselves).

Rationale for Shared Syntax

The rationale behind sharing the syntax for forwarding references and rvalue references lies in their seamless integration into template argument deduction and reference collapsing rules. By using the same syntax, universal references can be deduced as either lvalue references (T&) or rvalue references (T&&) based on the context.

This approach avoids the need for additional, more complex syntax. For example, if T&@ were used for universal references, the function parameter type could become T& or T&&, which would deviate from the actual type deduced by the compiler.

Rejection of Alternative Syntaxes

It is not clear whether alternative syntaxes for universal references were seriously considered during the standardization process. However, the consistent syntax aligns well with the existing type system and provides clarity in understanding the behavior of references in general.

In summary, the shared syntax for forwarding references and rvalue references allows for type deduction and reference collapsing to work seamlessly, avoiding the need for additional syntax or confusing grammar rules.

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