C++ High Performance

Named variables and r-values

So, when is the compiler allowed to move objects instead of copying? As a short answer, the compiler moves an object when the object can be categorized as an r-value. The term r-value might sound complicated, but in essence it is just an object which is not tied to a named variable, for either of the following reasons:

• It's coming straight out of a function
• We make a variable an r-value by using std::move(...)

The following example demonstrates both of these scenarios:

// Below, the object coming out of make_buffer is not tied to a variable// Therefore moved to x 
auto x = make_buffer();  
 
// Below, "x" is passed into std::move(...)// Therefore move-assigned to y 
auto y = std::move(x);  

Let's make this a little ...