c++ - bar(type(＆)[x])定义与bar(type(＆)[x])声明不匹配？

This question already has an answer here:

a constant in dependent base class make out-of-line definition not matched?

(1个答案)

在6个月前关闭。

这是Template class type alias failing substitution in member declaration的跟进
考虑以下代码:

// A
template <typename T>
struct foo {
    using type = unsigned;
   
    template <type x>
    void bar(type (&)[x]);
};
    
template <typename T>
template <typename foo<T>::type x>
void foo<T>::bar(type (&)[x]){}

gcc emits the following error:

<source>:13:6: error: no declaration matches 'void foo<T>::bar(foo<T>::type (&)[x])'
   13 | void foo<T>::bar(type (&)[x]){}
      |      ^~~~~~
<source>:8:10: note: candidate is: 'template<class T> template<unsigned int x> void foo<T>::bar(foo<T>::type (&)[x])'
    8 |     void bar(type (&)[x]);
      |          ^~~
<source>:4:8: note: 'struct foo<T>' defined here
    4 | struct foo {
      |        ^~~
Compiler returned: 1

clang:

<source>:13:14: error: out-of-line definition of 'bar' does not match any declaration in 'foo<T>'
void foo<T>::bar(type (&)[x]){}
             ^~~
1 error generated.
Compiler returned: 1

当我删除错误定义和候选对象中相同的内容时，我得到以下信息:

// B
template <typename T>
struct foo {
    using type = unsigned;

    template <type x>
    void bar();
};

template <typename T>
template <typename foo<T>::type x>
void foo<T>::bar(){}

这样编译就可以了(gcc/clang)
试图回答原始问题(达胡克(Darhuuk)，稍作修改)是:

// C
#include <type_traits>

template <typename T> struct length { using type = unsigned int; };    
template <typename T> using length_t = typename length<T>::type;

template <typename type>
class Object {
  template <length_t<Object<type>> length>
  void put(type (&)[length]);
};

template <typename type>
template <length_t<Object<type>> length>
void Object<type>::put(type (&)[length]) {}

int main() {}

lang似乎与原始代码和emits the error有类似的问题:

<source>:15:20: error: out-of-line definition of 'put' does not match any declaration in 'Object<type>'
void Object<type>::put(type (&)[length]) {}
                   ^~~
1 error generated.

而gcc compiles it without complaints。
谁对C是正确的？它是Clang中的错误还是gcc松懈？
为什么A不能编译B？

最佳答案

正如我在 Template class type alias failing substitution in member declaration中提到的:

CWG2, the ancient issue that nobody knows when it's posted, is still drafting, which means the match rule of out-of-definition is even unspecified. these weird mismatches are because of the different implementations of compilers.

关于c++ - bar(type(＆)[x])定义与bar(type(＆)[x])声明不匹配？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/64600329/

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