Why is `std::move` Called `std::move` if it Doesn't Move Anything?

Why Is std::move Named std::move?

Contrary to its name, std::move does not physically move anything; rather, it casts the object to an rvalue reference or, more specifically, an xvalue. The decision to name the function move was not to deceive or confuse but to make code more readable.

In the early stages of rvalue references, the std::swap function needed to be optimized for performance. The original method used explicit static_cast expressions, which obscured the underlying purpose of the code.

By introducing std::move, the explicit casts were replaced with syntax sugar that emphasized the intent of the code: to enable move semantics. Explaining the precise technical details, such as "cast to rvalue," would have raised additional questions, obscuring the main point.

The History of std::move

The history of std::move goes back to the proposal for rvalue references in 2002. The move function was initially introduced as syntax sugar for static_cast, with the understanding that few programmers at the time fully understood the connection between rvalues and move semantics.

As the C language evolved, the concept of rvalues was refined into what we know today as value categories. Using a different name, such as cast_to_xvalue, to more accurately describe the operation might have hindered readability.

What std::move Does

At its core, std::move simply casts an object to an xvalue. This cast has no impact on trivially movable objects, and for objects with move assignment operators, it ensures that the move assignment operator is called instead of the copy assignment operator.

In terms of generated object code, std::move has no impact for trivially movable objects. For objects with move assignment operators, it may alter the overload resolution. However, at run time, std::move effectively disappears, and its only impact is at compile time.

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