C++11标准中§12.6.2/2中单词"constructor's class"的解释

Question

作为健全性检查，有人可以确认 §12.6.2/2 中的 constructor's class 一词是否指的是委托构造函数吗？

12.6.2/2 声明：

Unless the mem-initializer-id names the constructor’s class, a non-static data member of the constructor’s class, or a direct or virtual base of that class, the mem-initializer is ill-formed.

Answer 1

是的。它表示与 mem-initializer-id 具有相同的 class 是有效的，这将使当前构造函数成为委托构造函数。这在 12.6.2/6 中有进一步解释：

If a mem-initializer-id designates the constructor’s class, it shall be the only mem-initializer; the constructor is a delegating constructor, and the constructor selected by the mem-initializer is the target constructor.

Answer 2

他们有。来自 delegating constructors proposal:

Change §12.6.2(2) as follows:

(...) Unless the mem-initializer-id names a non-static data member of the constructor's class, the constructor's class, or a a direct or virtual base of that class, the mem-initializer is ill-formed. (...)

新插入的文本在提案中用下划线代替了粗体，但我不能在 markdown 中这样做。它继续下去：

A mem-initializer-list can delegate to another constructor (the target constructor) of the constructor's class using any name that denotes the constructor's class itself. (...)

此措辞在最终标准 12.6.2 (6) 中发现，稍有改动：

A mem-initializer-list can delegate to another constructor of the constructor's class using any class-or-decltype that denotes the constructor's class itself. (...)

所以是的，所有这些都来自委派构造函数的提案，并且专门指构造函数委托。

Answer 3

在整个 [class.base.init] 中，"constructor" 指的是第 1 段中介绍的相同 "constructor"：

In the definition of a constructor for a class, initializers for direct and virtual base subobjects and non-static data members can be specified by a ctor-initializer, which has the form [...]

第2段说在a构造函数的定义中，mem-initializer-id（可以有多个mem-initializer-ids in a mem-initializer-list) 可以指三件事之一：

• 构造函数的class，即委托构造函数（第6段）
• 一个非静态数据成员，即S() : n{5}
• class 的直接或虚拟基础，即 S() : Base(5)（第 3 段）