Something that has been bugging me for a while is that there is no framework function as simple as string.Join( ) for, say, an array of integers. Or at least, there aren’t any that I’m aware of.

There are a bunch of ways to write this, of course, but I like this implementation using custom formatters that I’ve made most of all. It’s obviously not the most efficient way to do it, but I find it extremely useful.

// First, the class that is used as the public interface.
// This provides an object that does the heavy lifting.
public class EnumerableFormatProvider : IFormatProvider
{
    private static EnumerableFormatter _formatter =
        new EnumerableFormatter();

    private static EnumerableFormatProvider _default =
        new EnumerableFormatProvider();

    public static EnumerableFormatProvider Default
    {
        get { return _default; }
    }

    public object GetFormat(Type formatType)
    {
        if (formatType == typeof(ICustomFormatter))
        {
            return _formatter;
        }
        return null;
    }

    private EnumerableFormatProvider() { }
}

// Now the class that enumerates the objects and joins them up.
internal class EnumerableFormatter : ICustomFormatter
{
    public EnumerableFormatter() { }

    public string Format(string format, object arg,
                         IFormatProvider formatProvider)
    {
        if (arg == null)
        {
            return string.Empty;
        }

        IEnumerable e = arg as IEnumerable;
        if (e == null)
        {
            return arg.ToString();
        }
        else
        {
            StringBuilder sb = new StringBuilder();
            bool first = true;

            IEnumerator en = e.GetEnumerator();
            while (en.MoveNext())
            {
                if (!first)
                {
                    sb.Append(format);
                }
                first = false;
                sb.Append(en.Current.ToString());
            }
            return sb.ToString();
         }
    }
}

Here’s one example of how you might use it.

static void Main(string[] args)
{
    // prints "1234"
    Console.WriteLine(
        string.Format(EnumerableFormatProvider.Default, "{0}",
        new int[] { 1, 2, 3, 4 })
    );

    // prints "1,2,3,4"
    Console.WriteLine(
        string.Format(EnumerableFormatProvider.Default, "{0:,}",
        new int[] { 1, 2, 3, 4 })
    );
}

Tags: .NET, C#

This entry was posted on Monday, January 3rd, 2005 at 8:59 pm and is filed under .NET, Microsoft Technology. You can follow any responses to this entry through the feed . You can leave a response, or trackback from your own site.