演绎指南，模板和子对象:哪个编译器正确? [英] Deduction guides, templates and subobjects: which compiler is right?

问题描述

请考虑以下代码段:

struct S {
    S() {}

    template<typename B>
    struct T {
        T(B &&) {}
    };

    template<typename B>
    T(B &&) -> T<B>;
};

int main() {
    S::T t{0};
}

C语接受，而GCC

Clang accepts it while GCC rejects the code with the following error:

prog.cc:10:5:错误:推论指南'S :: T(B&&)-> S :: T'必须在名称空间范围内声明

prog.cc:10:5: error: deduction guide 'S::T(B&&) -> S::T' must be declared at namespace scope

这是有效的代码吗?GCC或Clang是哪种编译器是正确的?

Is this valid code? Which compiler is right, GCC or Clang?

推荐答案

根据 http://en.cppreference.com/w/cpp/language/class_template_argument_deduction

用户定义的推导指南必须命名类模板，并且必须在类模板的相同语义范围内引入(可以是名称空间或封闭类)，并且对于成员类模板，必须具有相同的访问权限，但是扣除指南不属于该范围.

User-defined deduction guides must name a class template and must be introduced within the same semantic scope of the class template (which could be namespace or enclosing class) and, for a member class template, must have the same access, but deduction guides do not become members of that scope.

所以c似乎是正确的.

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