What Member Function Specifiers Are &, &&, and const& Used for in C ?

Member Function Specifiers in C : const&, &, and &&

Introduction:

In C , member functions can be declared with various specifiers. Aside from the familiar const, two additional specifiers, & and &&, have been introduced in the C 11 standard. This article aims to clarify the meanings and usages of these specifiers.

Understanding the Specifiers:

const&:

• This specifier indicates that the member function can be invoked on both const and non-const objects.
• However, it requires the object to be an lvalue (i.e., not a temporary or rvalue).

Example:

<code class="cpp">class A {
public:
    const A& operator*() const&; // Can be invoked on both const and non-const lvalues
};</code>

&:

• This specifier indicates that the member function can be invoked only on non-const objects.
• It also requires the object to be an lvalue.

Example:

<code class="cpp">class A {
public:
    A& operator*() &; // Can be invoked only on non-const lvalues
};</code>

&&:

• This specifier indicates that the member function can be invoked only on rvalue objects (i.e., temporaries or expressions).
• In other words, it skips the class scope and directly invokes the member function on the temporary object.

Example:

<code class="cpp">class A {
public:
    A&& operator*() &&; // Can be invoked only on rvalues
};</code>

Usage in Practice:

These specifiers allow for more specific and efficient member function definitions.

• const&: Useful for functions that don't modify the object or guarantee that the result will not be used to modify the object.
• &: Ensures that the object is non-const and prevents the compiler from automatically creating a temporary copy.
• &&: Optimizes performance by avoiding object creation and destruction for temporary objects.

Conclusion:

The const&, &, and && specifiers provide greater control and flexibility when defining member functions in C . Understanding their nuances allows programmers to write more efficient and robust code.

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