为什么编译器在给定 const char * 作为模板化参数的类型时选择 bool 而不是 string_view？

Question

#include <iostream>

struct A
{
    void update(bool const & v)
    {
        std::cout << std::boolalpha << v << std::endl;
    }

    void update(std::string_view v)
    {
        std::cout << v << std::endl;
    }
};


template <typename T>
void update(T const & item)
{
    A a;
    a.update(item);
}


int main()
{
    const char * i = "string";
    update(i);
}

当我用 const char * 调用更新时，编译器用 bool 参数而不是 string_view 调用函数？！为什么？？！

Answer 1

从 const char * 到 std::string_view 的转换（通过 constructor of std::string_view) is a user-defined conversion; which is a worse match than the standard conversion (the implicit conversion from const char* to bool) in overload resolution.

1) A standard conversion sequence is always better than a user-defined conversion sequence or an ellipsis conversion sequence.