c++ - 具有 bool 模板参数的成员函数的显式模板实例化

Question

我不确定当template参数是 bool(boolean) 类型而不是类型时如何显式实例化模板。我将代码简化为一个简短的示例。我从clang(使用-std=c++2a)得到的错误是:

Vec.cpp:13:20: error: explicit instantiation of 'angle' does not refer to a function template, variable template, member function, member class, or static data
      member
template bool Vec::angle<false>;

这是我的代码:

Vec.hpp:

class Vec {
public:
    template <bool degrees>
    double angle(void);
};

Vec.cpp:

#include "Vec.hpp"
template <bool degrees>
double Vec::angle(void) {
    if constexpr (degrees) {
        // degree math
        return 360;
    } else {
        // radian math
        return 2*3.14;
    }
}

template bool Vec::angle<false>; // I don't understand what I should put here

main.cpp:

#include "Vec.hpp"
#include <iostream>

int main(void) {
    Vec v;
    std::cout << v.angle<false>() << "\n";
    return 0;
}

Answer 1

template double Vec::angle<false>();
template double Vec::angle<true>();

错字加上您也错过了 ()。