可以删除非特殊C ++成员函数（或默认）吗？ [英] Can non-special C++ member functions be deleted (or defaulted)?

问题描述

对于特殊成员 = default 和 = delete 已收到很多关注构造函数，析构函数，复制和移动）。可以与其他函数一起使用 = default 和 = delete 成员函数，自由函数和运算符等。

我可以理解， = default 特别成员;因为它基本上是说使用编译器生成的默认。默认值需要在编译器能够生成之前进行明确定义。据我所知，只有特殊成员有这些预定义的默认值。

= delete

• 可以<$>



• 可以在（成员，非成员，运算符）上使用什么函数类型？c $ c> = delete

任何函数都可以声明为已删除（ 使用 = delete ）。该标准不施加任何限制。这由C ++ 11 [dcl.fct.def.delete]覆盖。它甚至给出了一个删除的运算符新的示例。





默认的函数，另一方面， 受限于[dcl.fct.def.default]§1，如下所示：




1 ...是明确默认的







• 是一个特殊的成员函数，


• 除了可能不同的 ref-qualifiers ，除了在复制构造函数或复制赋值运算符的情况下，参数类型可以是引用
  非const T ，其中 T 是成员函数类的名称）
  ，就像它已被隐式声明一样，


• 没有默认参数。








<






• 默认构造函数


• 复制构造函数


• 移动构造函数


• 复制赋值运算符


• 移动赋值运算符


• 析构





A lot of attention has been received by = default and = delete with respect to the special members (default constructor, destructor, copy and move). Can = default and = delete be used with other functions; member functions, free functions and operators etc.?

I can understand that = default would probably not be allowed outside the special members; since it is basically saying use the compiler generated default. The default would need to be clearly defined before the compiler is able to generate it. As far as I know, only the special members have these pre-defined defaults.

What about = delete; it is basically saying that the function is declared, but the implementation is explicitly not defined.

• Can = delete be used with functions other than the special members?
• What function types can it be used on (members, non-members, operators etc.)?
• Or conversely, where (or when) is = delete prohibited from being used? Are there any restrictions on its use?

解决方案

Any function whatsoever can be declared as deleted (using = delete). The standard does not impose any restrictions. This is covered by C++11[dcl.fct.def.delete]. It even gives an example of a deleted operator new.

Defaulted functions, on the other hand, are limited by [dcl.fct.def.default]§1 as follows:

1 ... A function that is explicitly defaulted shall

• be a special member function,
• have the same declared function type (except for possibly differing ref-qualifiers and except that in the case of a copy constructor or copy assignment operator, the parameter type may be "reference to non-const T", where T is the name of the member function’s class) as if it had been implicitly declared, and
• not have default arguments.

The "special member functions" referenced in the first bullet point are (as per [special]§1):

• default constructor
• copy constructor
• move constructor
• copy assignment operator
• move assignment operator
• destructor

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