What are C 11 Rvalue References (T&&) and How Do They Improve Performance?

Unveiling the Rvalue Reference: T&& in C 11

C 11 brings an exciting addition to its syntax: the double ampersand symbol, T&&, when used in declaring variables. Initially perplexing, let's delve into its true nature and uncover its significance.

The Essence of an Rvalue Reference

T&& represents an rvalue reference, as defined in the standards proposal. Simply put, it enables a reference variable to bind to an rvalue, or a temporary value. This departs significantly from traditional C 03 references (now called lvalue references in C 11), which could only bind to lvalues or named variables.

Empowering Move Semantics

Rvalue references unlock the power of move semantics. A move constructor and move assignment operator can now be defined that accepts rvalue references. Move constructors are designed to transfer resources from a temporary object to a new object, rather than copying them. This optimization eliminates unnecessary copying and enhances performance.

Facilitating Perfect Forwarding

rvalue references play a vital role in perfect forwarding, which ensures proper propagation of argument types in templated functions. By utilizing std::forward, template arguments can be deduced accurately, allowing generic factory functions to be created that handle both lvalues and rvalues seamlessly.

Key Properties of Rvalue References

Understanding the following properties is essential:

• Binding Preference: Lvalues prefer binding to lvalue references, while rvalues prefer rvalue references.
• Implicit Binding: rvalue references can automatically bind to rvalues and temporaries generated by implicit conversions.
• Named versus Unnamed: Named rvalue references are lvalues, while unnamed rvalue references are rvalues.

A Glimpse into Usage

To illustrate an example:

T&& r = T();

In this code, the reference r can bind to the temporary object created by T(). This would initialize r with a reference to the temporary object's resources, optimizing memory usage and performance.

Unleashing the Power

Rvalue references empower C 11 developers with move semantics and perfect forwarding, offering significant performance enhancements and code flexibility. By understanding their nature and properties, you can unlock their potential to enhance the efficiency and elegance of your code.

The above is the detailed content of What are C 11 Rvalue References (T&&) and How Do They Improve Performance?. For more information, please follow other related articles on the PHP Chinese website!