#include <random>
#include <iostream>
template<typename T, typename Tengine=std::mt19937> 
class RandOne {
  std::uniform_real_distribution<T> dist_;
  Tengine eng_;
  public:
  /* constructor w. non-deterministic seed */
  RandOne() : dist_(0,1) {
    std::random_device rd;
    eng_.seed(rd());
  }
  /* random float [0:1[ */
  T operator()() {
    return dist_(eng_);
  }
};

int main() {
  RandOne<double> r;
  std::cout << r(); // -> random double in range [0:1[
}