How to combine two methods with the same logic into a generic method

Question

I've two method:

        static int SumInt(List<string> list)
        {
            return list.Select(o => int.Parse(o)).Sum();
        }

        static float SumFloat(List<string> list)
        {
            return list.Select(o => float.Parse(o)).Sum();
        }

How can i get a generic method such as static T Sum<T>(List<string> list) where T:struct{},or a method with a ValueType return: static ValueType Sum(List<string> list){} The key point is not how to convert, but how to sum a struct or ValueType.

Answer 1

I would use a Dictionary<Type, Delegate> to hold the delegate that can do the computation. You then just have to register the correct delegates at run-time and it works quite easily.

private static Dictionary<Type, Delegate> _registry = new Dictionary<Type, Delegate>();

public static void Register<S, T>(Func<string, S> parse, Func<IEnumerable<S>, T> aggregate)
{
    _registry[typeof(T)] = (Func<IEnumerable<string>, T>)(xs => aggregate(xs.Select(parse)));
}

public static T Sum<T>(List<string> list) =>
    ((Func<IEnumerable<string>, T>)_registry[typeof(T)])(list);

Now I can write this code:

Register(int.Parse, Enumerable.Sum);
Register(float.Parse, Enumerable.Sum);

var sourceIntegers = new List<string>() { "1", "2", "3" };
var sourceFloats = new List<string>() { "1.1", "2.2", "3.3" };

Console.WriteLine(Sum<int>(sourceIntegers));
Console.WriteLine(Sum<float>(sourceFloats));

The output I get is this:

6
6.6

What makes this approach interesting is that I can do this:

Register(
    x => new XElement("value", x),
    xs => new XDocument(new XElement("list", xs)));
    
Console.WriteLine(Sum<XDocument>(sourceIntegers));

That outputs:

<list>
  <value>1</value>
  <value>2</value>
  <value>3</value>
</list>