When Are `const Foo&&` Rvalue References Useful in C ?

Const Rvalue References: A Practical Perspective

In C , one might question the utility of rvalue references to const objects. To delve deeper into this topic, let's analyze the question: "Are there any scenarios where const Foo& & can be advantageous, assuming Foo is a class type?"

Surprisingly, const rvalue references offer distinct benefits. The C 0x draft itself exemplifies their usage within the following code:

template <class T> void ref(const T& &) = delete;
template <class T> void cref(const T& &) = delete;

These overloads effectively prevent other functions, such as ref(T&) or cref(const T&), from binding to rvalue objects. This guarantees the intended behavior of these functions.

In the official standard document N3290, which is not publicly available, the same code is present in section 20.8:

template <class T> void ref(const T& &) = delete;
template <class T> void cref(const T& &) = delete;

Moreover, in the most recent draft, N3485, these const rvalue reference overloads are still present in section 20.8, highlighting their continued relevance.

Thus, while one might initially assume const rvalue references lack utility, their practical applications within the C standard and other contexts underscore their significance.

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