删除构造函数的C ++ 14值初始化

问题描述

我有一些误解：

让我们将struct A的默认构造函数标记为已删除：

  struct A 
 {
 A（）= delete; 
}; 
  

下一条指令格式正确，效果如何？：

  A a {}; 
  

从：

但是默认初始化的效果是：

还是聚合初始化？
谢谢！

解决方案

您的 struct A / p>

• 一个类类型包含：
  
  
  
  • 没有用户提供的构造函数
    
  • 没有私人或受保护的非静态资料成员，
  
  
  • 没有基类，
  
  
  • 没有虚拟成员函数。
  
  

聚合类型，根据第8.5.1 / 1节提供的定义。

然后聚合初始化的值优先于值初始化。该标准说，聚合初始化优先于价值初始化（草案N3936，第8.5.4 / 3，第201页）（强调我）

根据为什么已删除的构造函数不会计为用户定义的注释中的要求， （N3936草案，第8.4.2 / 5页，第198页）：

I have some misunderstanding:

Let's mark default constructor of struct A as deleted:

struct A
{
  A() = delete;
};

The next instruction is well-formed and what's that effect?:

A a{};

From cppreference value initilization:

but then the effect of default initialization is:

Or it's aggregate initialization?Thanks!

解决方案

Your struct A is :

• a class type that has:
  • no user-provided constructors,
  • no private or protected non-static data members,
  • no base classes,
  • no virtual member functions.

It therefore qualifies as an aggregate type, according to the definition provided by § 8.5.1/1.

Then comes the priority of aggregate initialization over value initialization. The standard says that aggregate initialization has precedence over value intialization (draft N3936, § 8.5.4/3, page 201) (emphasis mine)

As requested in the comments on why a deleted constructor does not count as user-defined, here is what the standard says (draft N3936, § 8.4.2/5, page 198):

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