C# List.ConvertAll and exception

Question

if ConvertAll throw an exception on one element, can i just skip this element and continue to the next element?

Answer 1

No. The exception will need to be handled somewhere. If you expect exceptions to happen in the converter (and this is OK for the application), you must have a try-catch within the converter (the following code sample will return null for failed conversions):

List<string> input = new List<string> { "1", "2", "three", "4" };

List<int?> converted = input.ConvertAll(s =>
{
    int? result = null;
    try
    {
        result = int.Parse(s);
    }
    catch (Exception) { }

    return result;
});

(yes, I know I should have used int.TryParse, but that would not throw an exception...)

However, eating exceptions like that always gives the smell of a workaround, and is nothing I would like to have in my code.

Answer 2

If you need to skip the throwing element entirely ConvertAll will not result for you, however you can implement a helper method for "robust enumeration". Something like this:

public static void Main(string[] args)
{
    var integers = new List<int>() { 1, 2, -5 };
    Converter<int, string> converter = x =>
    {
        if (x < 0)
            throw new NotSupportedException();

        return x.ToString();
    };

    // This code would throw
    //var result1 = integers.ConvertAll(converter).ToArray();
    //Console.WriteLine(String.Join(Environment.NewLine, result1));

    // This code ignores -5 element
    var result2 = RobustEnumerating(integers, converter).ToArray();
    Console.WriteLine(String.Join(Environment.NewLine, result2));
}

public static IEnumerable<K> RobustEnumerating<T, K>(IEnumerable<T> input,
    Converter<T, K> converter)
{
    List<K> results = new List<K>();
    foreach (T item in input)
    {
        try
        {
            results.Add(converter(item));
        }
        catch { continue; }
    }
    return results;
}

I would only do this if returning null or other unique value for failed conversions and then filtering the result to exclude those values is not applicable.