模板专用化-模板参数太少[closed]

所以我在玩模板专业化,遇到了一个问题。我在看 this 同时编写以下代码。

我减少了它,但基本上我对calc的模板做了一些不正确的事情,我不确定是什么。在所有其他帖子中,我都看到人们在专业课之前忘记了“模板”,但我不认为这是导致我问题的原因。有什么建议吗?

#include <type_traits>
#include <iostream>

template <typename T, bool isDouble = std::is_same<T, double>::value>
struct precision
{ 
    typedef T p_type;
    /* some stuff here*/
};

template <typename T>
struct precision<T, false>
{ 
    typedef T p_type;
    /* some stuff here*/
};

template <typename P>
struct is_double
{ 
    static const bool value = std::is_same< typename P::p_type, double >::value;
};

template <typename T, typename SP, typename DP>
struct calc
{
    static_assert(!is_double<SP>::value, "SP is not single precision");
    static_assert(is_double<DP>::value, "DP is not double precision");
};

template <typename T, typename SP>
struct calc<T, SP, precision<double>>
{
    static_assert(!is_double<SP>::value, "SP is not single precision");
};

template <typename T, typename DP>
struct calc<T, precision<float>, DP>
{
    static_assert(is_double<DP>::value, "DP is not double precision");
};

template <typename T>
struct calc<T, precision<float>, precision<double>>
{ };

int main()
{
    calc<int> t1; //"too few template arguments"
    calc<int, precision<double> > t2; //"too few template arguments"
    calc<int, precision<float> > t3; //"too few template arguments"
    calc<int, precision<float>, precision<double>> t4;
}