在std :: accumulate C ++中使用模板Lambda表达式？

Question

Is there to templatize the "ints" in the lambda function below in the case that there was a standard container of doubles or floats, etc.? I have searched the world over for help with this. I even asked for the help of my professor who says it is possible but is to cryptic about the answer.

template <typename T>
   float mean(T &container)
   {
     auto sum = std::accumulate(container.begin(), container.end(), 0/*initial value*/,
     [](int total, int cur)
     {
          return total+cur;
     }//end of lambda
   );//end of accumulate
   return static_cast<float>(sum) / container.size(); //to find the mean
}//end of mean

Thanks in advance.

Answer 1

There is typically a way to get the type of the contained data from a container.

For eg you could replace the int s in that function with T::value_type which should support all containers which expose such a typedef.

This wont work for types such as map but you can specialize for it if you want to support them.

Answer 2

But it seems to me that writing such a function that way may induce loss of data For example

std::vector<float> vf;
vf.push_back(1.3);
vf.push_back(1.5);
vf.push_back(1.3);
vf.push_back(1.123);
vf.push_back(1.526);
float m=mean(vf);

will always return 1

The answer here >>> compute mean using std::accumulate fails in the Edit part is not really true as if I change vf.push_back(1.3); into vf.push_back(3.3); I'll obtain the wished result.