I have created a helper function which accepts a string array as input and the index of the column as selected output.

public static List<T> GetByIndex<T>(string[] data, int index)
{
    List<T> list = new List<T>();
    foreach (var item in data)
    {
        if (item.Contains("|"))
        {
            string[] s = item.Split("|");
            list.Add(s[index]);
        }
    }
    return list;
}

At line list.Add(s[index]); i get the error Cannot convert from 'string' to 'T'.

How can i make this method generic?

The function should return string or integer or even maybe boolean

CodePudding user response：

How can i make this method generic?

You shouldn't. You're only dealing with strings so make the method return a List<string>

public static List<string> GetByIndex(string[] data, int index)
{
    var list = new List<string>();
    foreach (var item in data)
    {
        if (item.Contains("|"))
        {
            string[] s = item.Split("|");
            list.Add(s[index]);
        }
    }
    return list;
}

If you need to also support int then just make an overload which returns a List<int> and use int.Parse / int.TryParse.

CodePudding user response：

It seems that you don't want generic T at all: what is the expected output for, say, T == IComparer<DateTime>?

I suggest getting rid of T and returning List<string>:

public static List<string> GetByIndex(string[] data, int index) {
  // Public method's arguments validation
  if (data is null)
    throw new ArgumentNullException(nameof(data));
  if (index < 0)
    throw new ArgumentOutOfRangeException(nameof(index));

  List<string> list = new List<string>();

  foreach (string item in data) {
    // Do not forget about nulls
    if (item != null) {
      // We can stop earlier on Split: 
      // if, say, index == 2 we don't want all 12345 items
      string[] s = item.Split('|', index   2);

      // s can well be too short 
      if (s.Length > index)
        list.Add(s[index]); 
    }
  }

  return list;
}

CodePudding user response：

If you want to return a List<T>, you need to provide some way of converting each string into a T.

Such as:

public static List<T> GetByIndex<T>(
    string[] data,
    int index,
    Func<string, T> convertItem)
{
    List<T> list = new List<T>();
    foreach (var item in data)
    {
        if (item.Contains("|"))
        {
            string[] s = item.Split("|");
            list.Add(convertItem(s[index]));
        }
    }
    return list;
}

And you could provide convenience overloads for the types you commonly use.

For example:

public static List<int> GetIntByIndex(string[] data, int index)
{
    return GetByIndex(data, index, int.Parse);
}