tommy.blog

I see people use string.Format(formatProvider, "{0}", value) or string.Format(formatProvider, "{0:formatSpecifier}", value), just to format a value (int, double, ...). I used to do this to, until I looked at how string.Format works (using Reflector). Apparently, a StringBuilder-object is created, and the "{0:...}" is parsed, a lot of appending happens and finally the stringBuilder.ToString() is returned. Here's a function that does the same. Basically, it just does the same as inside StringBuilder.AppendFormat, but without all the parsing, creating and appending. It's a lot faster, and creates less temporary objects.

public static string Format(object value, IFormatProvider formatProvider, string formatSpecifier)
{
   if (formatSpecifier.Length == 0)
      return value.ToString();

   if (formatProvider == null)
      formatProvider = System.Globalization.CultureInfo.CurrentCulture;

   ICustomFormatter formatter = formatProvider.GetFormat(typeof(ICustomFormatter)) as ICustomFormatter;
   if (formatter != null)
      return formatter.Format(formatSpecifier, value, formatProvider);

   IFormattable formattable = value as IFormattable;
   if (formattable != null)
      return formattable.ToString(formatSpecifier, formatProvider);

   return value.ToString();
}