Generic method for converting string array into list ...

Question

I would like to create a function that will return list of type that is specified by me at run time. I tried something along this line:

  public static List<T> GetMyList<T>(string[] itemList)
  {
     List<T>  resultList = new List<T>(itemList.Length);
     return resultList.AddRange(itemList);
  }

But this doesn't work. Obviously I don't fully understand how to pass a type to be converted to. Any help would be appreciated it.

Edit: It looks like that it is not possible, but here is more info. String array will contain numbers and I would like to convert those numbers sometimes into int, sometimes into short. Idea behind is to have a generic function that will attempt to convert items into whatever type list I tell it.

Answer 1

this doesn't work because system has no idea how to convert string to generic T. Also even if it is known, it will not work, because C# (prior to 4) doesn't have type covariance. So use either foreach to copy and convert elements one by one or use Select from Linq

Answer 2

You need to provide a method to convert a string into a T - you can do this using a Func<string, T>:

public static List<T> GetMyList<T>(string[] itemList, Func<string, T> conversionFunc)
{
    return itemList.Select(conversionFunc).ToList();
}

e.g.

List<int> ints = GetMyList(new[] { "1", "2", "3" }, s => int.Parse(s));

Answer 3

My first thought is that this won't work because not every object type can be constructed from a string. Perhaps you want something with a signature more like:

public static List<T> GetMyList<T>(T[] itemList)
{
  List resultList = new List(itemList.Length);
  foreach (t in itemList)
  {
    resultList.add(t);
  }
  return resultList;
}

(forgive my syntax. I don't have a compiler handy right now to check it.)

Answer 4

Similar to Lee's but more generic...

public static class Tools
{
    public static List<TResult> ToList<T, TResult>(
       this IEnumerable<T> input,
            Func<T, TResult> conversion)
    {
        return input.Select(conversion).ToList();
    }
    public static List<TResult> ToList<T, TResult>(
        this IEnumerable<T> input,
             Func<T, int, TResult> conversion)
    {
        return input.Select(conversion).ToList();
    }
}

class Program
{
    static void Main(string[] args)
    {
        var input = new[] { "1", "2", "3" };

        var ret = input.ToList(i => int.Parse(i));
        // 1,2,3

        var ret2 = input.ToList((i,j) => int.Parse(i) + j * 10);
        // 1,12,23
    }
}