C 11中ConstExpr对象中的可变成员

A conditional-expression e is a core constant expression unless the evaluation of e,following the rules of the abstract machine (1.9),would evaluate one of the following expressions:

• […]
• an lvalue-to-rvalue conversion (4.1) unless it is applied to
  • […]
  • a non-volatile glvalue that refers to a non-volatile object defined with constexpr,or that refers to a non-mutable sub-object of such an object,or

因此,此代码在C 14中不正确：

class A {
    public:
        mutable int x;
};

int main(){

    constexpr A a = {1};
    constexpr int y = a.x;

    return 0;
}

但是,它在C 11中是否正确？

这是缺陷报告(CD3)1405,他们建议添加不可变：

Currently,literal class types can have mutable members. It is not clear whether that poses any particular problems with constexpr objects and constant expressions,and if so,what should be done about it.

所以我会说这是正确的C 11代码.然而,我用-std = c 11尝试了Clang和GCC,并且都输出了一个错误,表示在常量表达式中不允许使用可变变量.但是这个约束是在C 14中添加的,它不在C 11中.

有谁知道C 11中的代码是否正确？

另见缺陷报告(CD3)1428.