What are C 11 Rvalue References (&&) and How Are They Used?

Use of '&&' (Double Ampersand) in C 11

C 11 introduced a new type of reference called an rvalue reference, indicated by the double ampersand symbol "&&".

What is an Rvalue Reference?

An rvalue reference is a reference that can bind to an rvalue, which is an expression or temporary value that is not assigned to a named variable. This is in contrast to lvalue references, which bind to named variables or objects.

Benefits of Rvalue References

Rvalue references provide several benefits, including:

• Move Semantics: They allow for efficient "move" operations, which transfer resources from one object to another without copying.
• Perfect Forwarding: They enable template functions to correctly forward arguments based on their rvalue/lvalue status.

Syntax and Usage

T&& var; // Declares an rvalue reference to T named 'var'

When to Use Rvalue References

Use rvalue references in the following scenarios:

• Move Constructors and Operators: To define functions that can efficiently move resources from an rvalue.
• Perfect Forwarding: To create generic functions that can handle rvalues and lvalues transparently.
• Implicit Conversions: To allow rvalue references to bind to temporaries that result from implicit conversions.

Important Properties

• Overload Resolution: Lvalue references are preferred for lvalues, while rvalue references are preferred for rvalues.
• Implicit Binding: Rvalue references can bind to rvalues and temporaries without explicit conversion.
• Value Category: Named rvalue references are lvalues, while unnamed rvalue references are rvalues.

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