c++ - 删除的构造函数 - MSVC 报告错误，Clang 没有

Question

考虑以下代码:

class SILPassPipelinePlan final {
public:
  SILPassPipelinePlan() = default;
  ~SILPassPipelinePlan() = default;
  SILPassPipelinePlan(const SILPassPipelinePlan &) = default;
  SILPassPipelinePlan(SILPassPipelinePlan &&) = delete;

  SILPassPipelinePlan x() {
    SILPassPipelinePlan P;

    return P;
  }
};

int main() {
  return 0;
}

MSVC 报如下错误:

1>consoleapplication2.cpp(13): error C2280: 'SILPassPipelinePlan::SILPassPipelinePlan(SILPassPipelinePlan &&)': attempting to reference a deleted function

1>consoleapplication2.cpp(8): note: see declaration of 'SILPassPipelinePlan::SILPassPipelinePlan'

Clang 和 GCC 没有。

从规范的角度来看，哪个编译器是正确的？这是 MSVC 错误还是 Clang 错误？

MSVC 来自最新的 Visual Studio 2015 Update 3，Clang 是 3.9.0 版本。

Answer 1

C++11 在某些场景中引入了隐式移动— yours included :

In the following copy-initialization contexts, a move operation might be used instead of a copy operation:

• If the expression in a return statement ([stmt.return]) is a (possibly parenthesized) id-expression that names an object with automatic storage duration declared in the body or parameter-declaration-clause of the innermost enclosing function or lambda-expression, or

• […]

overload resolution to select the constructor for the copy is first performed as if the object were designated by an rvalue. If the first overload resolution fails, […]

Clang(唯一接受的实现，顺便说一句。)要么误解“失败”以包含已删除函数的选择，要么应用 [over.match.funcs]/8太松懈了。查看错误 31025 .