具有依赖名称(类型名称)的部分专业化 [英] partial specialization with dependent name (typename)

问题描述

我有以下简单的strinToTypeImpl函数，它将任何类型的字符串转换为模板类型.我担心的问题是编译器告诉我typename MyMatrix<T>::Vector3的部分专业化的事实:

I have the following simple strinToTypeImpl function which converts any kind of string into the template type. The problem I am concerned about is the fact that the compiler tells me for the partial specialization for typename MyMatrix<T>::Vector3 :

部分特化中未使用的模板参数T

我不能在专业化中使用从属名称吗?

namespace details
{

    template<typename T>
    struct stringToTypeImpl{
        bool operator()(T& t, const std::string& s)
        {
          std::istringstream iss(s);
          return !(iss >> t).fail();
        }
    };


    template<typename T>
    struct stringToTypeImpl< typename MyMatrix<T>::Vector3  >{ 

        // Replacing typename MyMatrix<T>::Vector3  by 
        // Eigen::Matrix<T,3,1> WORKS but why?

        bool operator()(typename MyMatrix<PREC>::Vector3 & t, const std::string& s)
        {
          stringToVector3<PREC>(t,s);
        }
    };
}

推荐答案

这只是问题的另一种形式，已经讨论了很多次:没有从类型X到类型T的一对一映射.这样的MyMatrix<T>::Vector3 == X.

This is just another form of the problem that has been discussed many times: There's no one-to-one mapping from types X to types T such that MyMatrix<T>::Vector3 == X.

简单的例子:

MyMatrix<double> { typedef Vector3 int; };
MyMatrix<float> { typedef Vector3 int; };

stringToTypeImpl<int> // Help, what is "T"?

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