小编Tms*_*tel的帖子

我把这个问题简化了一些:

http://coliru.stacked-crooked.com/a/2660b33492651e92

#include <iostream>
#include <string>
#include <type_traits>

template<typename C>
struct get_type
{
    C operator()() const = delete;
};

template<>
struct get_type<std::string>
{
    std::string operator()() const { return "asd"; }
};

template<>
struct get_type<size_t> {
    size_t operator()() const { return 6; }
};

struct S
{
    S(){}
    template<typename T>
    operator T() { return get_type<T>{}(); }
};

struct A
{
    A() :s{S{}}, n{S{}} {}
    std::string s;
    size_t n;
};

int main()
{
    A a;
    std::cout << "Spock out." << std::endl;
} …