我试图编写一个类，该类将用容器具有的类型的随机数填充容器：

template<typename random_type>
class rand_helper {
private:
    std::mt19937 random_engine;
    std::uniform_int_distribution<int> int_dist;
    std::uniform_real_distribution<double> real_dist;

public:
    rand_helper() = delete;
    rand_helper(random_type left_b, random_type right_b);
    random_type operator()();

};

template<typename random_type>
rand_helper<random_type>::rand_helper(const random_type left_b, const random_type right_b) :random_engine{ std::random_device{}()} {
    if constexpr (std::is_same_v<random_type, double>)
        real_dist(left_b, right_b );
    else
        int_dist( left_b, right_b );
}

template<typename random_type>
random_type rand_helper<random_type>::operator()() {
    if constexpr (std::is_same_v<random_type, double>)
        return real_dist(random_engine);
    else
        return int_dist(random_engine);
}

但是这里某处发生错误，因为当我调用 std::generate 时，我会收到很多错误：

template<typename T,typename vec_type = typename T::value_type>
void fill_contain(T& container,vec_type left_b=vec_type(0), vec_type right_b= vec_type(100)) {
    std::generate(std::begin(container),std::end(container), rand_helper<vec_type>(left_b ,right_b));   
}

我认为这可能是因为if constexpr但如果只是离开：

template<typename random_type>
random_type rand_helper<random_type>::operator()() {
    return int_dist(random_engine);
}

然后仍然返回相同的错误。这是我得到的错误列表：

Error   C2825   '_Urng': must be a class or namespace when followed by '::'
Error   C2510   '_Urng' : left of '::' must be a class / struct / union
Error   C2061   syntax error : identifier 'result_type'
Error   C2065   '_Ty1' : undeclared identifier
Error   C2923   'std::conditional_t' : '_Ty1' is not a valid template type argument for parameter '_Ty2'

函数调用是这样的：

 std::vector<int> for_sort;
    fill_contain(for_sort);

回答

template class rand_helper<int>;

template <typename T>
using uniform_distribution = std::conditional_t<
    std::is_integral_v<T>,
    std::uniform_int_distribution<T>, 
    std::uniform_real_distribution<T>
>;