c++ - 成员函数定义中的不完整类型

Question

[dcl.fct.def] p2状态:

The type of a parameter or the return type for a function definition shall not be an incomplete or abstract (possibly cv-qualified) class type in the context of the function definition unless the function is deleted.

还有 [class.mem] p7状态:

A class is considered a completely-defined object type (or complete type) at the closing } of the class-specifier. The class is regarded as complete within its complete-class contexts; otherwise it is regarded as incomplete within its own class member-specification.

鉴于此代码:

struct S
{
  // S is incomplete
  S f() {  /* S is complete in a function body */ return S(); }
  // S is incomplete 
};
// S is complete

一个 complete-class context值得注意的是，它不包括函数定义的 decl-specifier-seq，也不包括函数的声明符，但是，每个编译器都说这是可以的。什么措辞允许这样做，因为我找不到它？

Answer 1

引用链接中的第一项:

A complete-class context of a class is a

• function body ([dcl.fct.def.general]),

所以在任何方法的函数体内都被认为是一个完整的类上下文。据我所知，“函数定义的上下文”是函数体的同义词——与函数声明的上下文相反，函数声明的返回类型不需要完整。