First, if T is a class type and the initializer is a prvalue expression whose cv-unqualified type is the same class as T, the initializer expression itself, rather that a temporary materialized from it, is used to initialize the destination object: see copy elision
stock stock2 = stock(“fuch”, 2, 2.0); 屬於copy initialization 裡的語法形式(1)。
其中 stock(“fuch”, 2, 2.0) 屬於 prvalue expression，所以符合文中的情況：
First, if T is a class type and the initializer is a prvalue expression whose cv-unqualified type is the same class as T, the initializer expression itself, rather that a temporary materialized from it, is used to initialize the destination object: see copy elisioncopy elision是什麼意思，聽名字就很直觀了吧，然而這是C++17才被標準要求的語言層次上的最佳化，還得符合一些前提才會觸發這個最佳化。C++17以前做不做這個全靠編譯器的自覺，然而我所知道的幾個編譯器release模式下都有這個自覺，其中某些還提供了開關來讓你得以關閉這項最佳化。
至於第二句，我沒找到“ 分步定義 ”的文件在哪:)