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我將如何去做一個模板化的運算符與enable_if模板類的朋友？模板類與enable_if模板運算符的朋友
這裏是我的問題的一個例子：
#include <type_traits>
template<typename CHAR_TYPE>
class BasicString;
template<typename CHAR_TYPE, typename OTHER_CHAR_TYPE,
typename std::enable_if<((sizeof(CHAR_TYPE)==sizeof(OTHER_CHAR_TYPE))
&& std::is_integral<CHAR_TYPE>::value && std::is_integral<OTHER_CHAR_TYPE>::value), std::nullptr_t>::type = nullptr>
BasicString<CHAR_TYPE> operator+(const BasicString<CHAR_TYPE>& left, const BasicString<OTHER_CHAR_TYPE>& right);
template<typename CHAR_TYPE, typename OTHER_CHAR_TYPE,
typename std::enable_if<((sizeof(CHAR_TYPE)!=sizeof(OTHER_CHAR_TYPE))
&& std::is_integral<CHAR_TYPE>::value && std::is_integral<OTHER_CHAR_TYPE>::value), std::nullptr_t>::type = nullptr>
BasicString<CHAR_TYPE> operator+(const BasicString<CHAR_TYPE>& left, const BasicString<OTHER_CHAR_TYPE>& right);
template<typename CHAR_TYPE>
class BasicString
{
private:
CHAR_TYPE* characters;
size_t length;
template<typename OTHER_CHAR_TYPE,
typename std::enable_if<((sizeof(CHAR_TYPE)==sizeof(OTHER_CHAR_TYPE))
&& std::is_integral<CHAR_TYPE>::value && std::is_integral<OTHER_CHAR_TYPE>::value), std::nullptr_t>::type>
friend BasicString<CHAR_TYPE> operator+<CHAR_TYPE, OTHER_CHAR_TYPE>(const BasicString<CHAR_TYPE>& left, const BasicString<OTHER_CHAR_TYPE>& right);
template<typename OTHER_CHAR_TYPE,
typename std::enable_if<((sizeof(CHAR_TYPE)!=sizeof(OTHER_CHAR_TYPE))
&& std::is_integral<CHAR_TYPE>::value && std::is_integral<OTHER_CHAR_TYPE>::value), std::nullptr_t>::type>
friend BasicString<CHAR_TYPE> operator+<CHAR_TYPE, OTHER_CHAR_TYPE>(const BasicString<CHAR_TYPE>& left, const BasicString<OTHER_CHAR_TYPE>& right);
public:
BasicString()
: length(0),
characters((CHAR_TYPE*)std::malloc(sizeof(CHAR_TYPE)))
{
characters[0] = 0;
}
BasicString(const BasicString& str)
: length(str.length),
characters((CHAR_TYPE*)std::malloc(sizeof(CHAR_TYPE)*(str.length+1)))
{
for(size_t i=0; i<length; i++)
{
characters[i] = str.characters[i];
}
}
~BasicString()
{
delete characters;
}
};
template<typename CHAR_TYPE, typename OTHER_CHAR_TYPE,
typename std::enable_if<((sizeof(CHAR_TYPE)==sizeof(OTHER_CHAR_TYPE))
&& std::is_integral<CHAR_TYPE>::value && std::is_integral<OTHER_CHAR_TYPE>::value), std::nullptr_t>::type>
BasicString<CHAR_TYPE> operator+(const BasicString<CHAR_TYPE>& left, const BasicString<OTHER_CHAR_TYPE>& right)
{
BasicString<CHAR_TYPE> newStr;
CHAR_TYPE* characters = newStr.characters;
//do some stuff. irrelevant to question
}
template<typename CHAR_TYPE, typename OTHER_CHAR_TYPE,
typename std::enable_if<((sizeof(CHAR_TYPE)!=sizeof(OTHER_CHAR_TYPE))
&& std::is_integral<CHAR_TYPE>::value && std::is_integral<OTHER_CHAR_TYPE>::value), std::nullptr_t>::type>
BasicString<CHAR_TYPE> operator+(const BasicString<CHAR_TYPE>& left, const BasicString<OTHER_CHAR_TYPE>& right)
{
BasicString<CHAR_TYPE> newStr;
CHAR_TYPE* characters = newStr.characters;
//do some stuff. irrelevant to question
}
int main()
{
BasicString<char> str1;
BasicString<wchar_t> str2;
BasicString<char> newStr = str1 + str2;
return 0;
}
我知道，我可以使用的輔助函數或輔助類，但我寧願沒有，如果我能避免它。
當我編譯這個時，我得到的錯誤，運算符函數不能訪問該類的私有成員，這意味着我的結婚代碼不起作用。我將如何去結交這些功能？