StringBuilder, append string if conditions are met

Question

var sb = new StringBuilder ();

if (condition1) sb.Append ("one");
if (condition2) sb.Append ("two");
if (condition3) sb.Append ("three");
if (condition4) sb.Append ("four");
if (condition5) sb.Append ("five");

return sb.ToString ();

Any idea how to improve it? How to write less code, giving same result?

Answer 1

This code is fine. Keep it like this.

• Every attempt to use extension methods or others will only make this code less understandable and maintainable;
• There is no repeating code;
• As long as the conditions don't influence another, there is no way of shortening the ifs.

If you do want another option:

string s = 
   (condition1 ? "one" : null) + 
   (condition2 ? "two" : null) + 
   (condition3 ? "three" : null) + 
   (condition4 ? "four" : null) + 
   (condition5 ? "five" : null)
   ;

But let's be honest, does this make it better? No.

Answer 2

I prefer approach with simple DSLs definition, when it makes code simpler or more readable. Also "pipeline-style" expressions are awesome. In your case it can be written like this:

var str =
    new StringBuilder()
        .AppendIf(condition1, "one")
        .AppendIf(condition2, "two")
        .AppendIf(condition3, "forty two")
        .ToString();

With an extension method.

public static class StringBuilderExtensions
{
    public static StringBuilder AppendIf(
        this StringBuilder @this,
        bool condition,
        string str)
    {
        if (@this == null)
        {
            throw new ArgumentNullException("this");
        }

        if (condition)
        {
            @this.Append(str);
        }

        return @this;
    }
}

Approach is suitable here, if conditions are repeated. For example arg1 != null, arg2 != null, then AppendIfNotNull can be used.

Otherwise, think twice, because it looks quite similar to initial implementation, requires additional code, can be slower because of additional null checks and method invocations, and also you should create an AppendIf overload for every Append one.