C + + Primer notes--Understanding Std::move

The standard library move function is a good example of a template that uses rvalue references. The standard library defines std::move as follows:

Template <typename t>typename remove_reference<T>::type&& Move (t&& T) {     return static_cast<typename remove_reference<t>::type&&>(T);}

We consider the following code work process:

std::string S1 ("hi"= Std::move (string("hi "));    // correct, move data from a right value s2 = std::move (S1);                // correct, but after the assignment, the value of the S1 is indeterminate.

In the first assignment, the argument is the right value of type string, so the procedure is:

• Inferred T is of type string
• The type member of the remove_reference<string> is a string
• The move return type is string&&
• The type of the function parameter T of move is string&&

Thus, this invocation instantiates Move<string>, which is the function

string&& Move (string &&t)

In the second assignment, the argument is an lvalue, so:

• Infer that the type of T is string&
• The type member of the remove_reference<string&> is a string
• The move return type is string&&
• The type of the function parameter T of move is string& &&, which is folded into string&

Thus, this invocation instantiates move<string&>

string&& Move (string &t)

Typically, static_cast can only be used for other legitimate type conversions. But there is a concession rule for rvalue: although it is not possible to implicitly convert an lvalue to an rvalue reference, we can convert an lvalue to an rvalue using the static_cast display.

C + + Primer notes--Understanding Std::move