Although this may at first seem like only an efficiency concern ( and you normally don ' t want to concern yourself with efficiency tuning while you ' re designing and assembling your program ) , there ' s more at stake : as you ' ll see in the remainder of the chapter , a copy - constructor is required to pass an object by value , and this isn ' t always available 尽管初看起来,仅仅是一个与效率相关的难题(并且你在设计和装配程序时,一般不会想到通过调整效率来关心一下自己的程序) ,这更像是在赌博:本章余下的内容中你将会看到,通过传值方式需要给对象传递一个拷贝构造函数,但并不老是行得通。