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 盡管初看起來,僅僅是一個與效率相關(guān)的難題(并且你在設(shè)計和裝配程序時,一般不會想到通過調(diào)整效率來關(guān)心一下自己的程序) ,這更像是在賭博:本章余下的內(nèi)容中你將會看到,通過傳值方式需要給對象傳遞一個拷貝構(gòu)造函數(shù),但并不老是行得通。