部分专注于错误类型的非类型模板参数 [英] Partially specializing on non-type template parameter of the wrong type

问题描述

请考虑以下内容:

template <unsigned >
struct uint_ { };

template <class >
struct X {
    static constexpr bool value = false;
};

template <int I> // NB: int, not unsigned
struct X<uint_<I>> {
    static constexpr bool value = true;
};

int main() {
    static_assert(X<uint_<0>>::value, "!");
}

clang编译代码，而gcc不会.

clang compiles the code, gcc does not.

但是，在以下高度相关的示例中:

However, in the following highly related example:

template <unsigned >
struct uint_ { };

template <int I> // NB: int, not unsigned
void foo(uint_<I> ) { }

int main() {
    foo(uint_<0>{} );
}

两个编译器都拒绝了，没有匹配的函数调用foo. gcc的行为是一致的，clang的行为是不一致的-因此一个或另一个编译器对于一个或两个示例均存在错误.哪个编译器是正确的?

both compilers reject with no matching function call to foo. gcc's behavior is consistent, clang's is not - so one or the other compiler has a bug for one or both examples. Which compiler is correct?

推荐答案

GCC是正确的. [temp.deduct.type]/17 :

GCC is correct. [temp.deduct.type]/17:

如果P具有包含<i>的形式，并且 A的对应值不同于i的类型，推导失败.

If P has a form that contains <i>, and if the type of the corresponding value of A differs from the type of i, deduction fails.

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