内置类型的赋值运算返回对右(还是左??)操作数的引用
The return type from the assignment operator should be the same as the return from assignment for the built-in types (Section 5.4.1, p. 160). Assignment to a built-in type returns a reference to its left-hand operand. Therefore, the assignment operator also returns a reference to the same type as its class.赋值操作符的返回类型应该与内置类型赋值运算返回的类型相同(第 5.4.1 节)。内置类型的赋值运算返回对[color=#FF0000]右[/color]操作数的引用,因此,赋值操作符也返回对同一类类型的引用。