String.Format parameter order annoyance

Question

it's really annoying how C# seems to force you to explicitly name the index of every parameter in String.Format, if you want to add another parameter somewhere you either have to re-index the string or put your new parameter at the end.

Is there a way to get C# to do this automatically?

e.g. (I know this is pointless pedants, it's just an example :)

I start with:

String.Format("{0} {1} {1} {2} {3}", a, b, c, d)

if I want to add a parameter at the beginning I can do one of the following:

String.Format("{4} {0} {1} {1} {2} {3}", a, b, c, d, e)
String.Format("{0} {1} {2} {2} {3} {4}", e, a, b, c, d)

in Delphi for example I could do the equivalent of this:

String.Format("{} {} {} {2} {} {}", e, a, b, c, d)

Answer 1

Well, there's nothing in C# to do this automatically for you. You could always write your own method to do it, but frankly I'd find it less readable. There's a lot more thinking to do (IMO) to understand what your final line does than the previous one. When you hit the {2} you've got to mentally backtrack and replace the previous item with {3} to skip the {2} etc.

Personally I prefer code which takes a bit longer to type, but is clear to read.

Answer 2

As of Visual Studio 2015 you can side step this issue using Interpolated Strings (its a compiler trick, so it doesn't matter which version of the .net framework you target).

The code then looks something like this

string txt = $"{person.ForeName} is not at home {person.Something}"; 

I think it makes the code more readable and less error prone.

Answer 3

The function you request is not part of the framework. Here's a nice Extension Method I've found that provides named parameters c#. I think Marc Gravell posted it or one of those other SO gurus.

        static readonly Regex rePattern = new Regex(@"\{([^\}]+)\}", RegexOptions.Compiled);


    /// <summary>
    /// Shortcut for string.Format. Format string uses named parameters like {name}.
    /// 
    /// Example: 
    /// string s = Format("{age} years old, last name is {name} ", new {age = 18, name = "Foo"});
    ///
    /// </summary>
    /// <param name="format"></param>
    /// <param name="values"></param>
    /// <returns></returns>
    public static string FN<T>(this string pattern, T template)
    {
        Dictionary<string, string> cache = new Dictionary<string, string>();
        return rePattern.Replace(pattern, match =>
        {
            string key = match.Groups[1].Value;
            string value;

            if (!cache.TryGetValue(key, out value))
            {
                var prop = typeof(T).GetProperty(key);
                if (prop == null)
                {
                    throw new ArgumentException("Not found: " + key, "pattern");
                }
                value = Convert.ToString(prop.GetValue(template, null));
                cache.Add(key, value);
            }
            return value;
        });
    }