[C#] Extension methods

FormatString

public static string FormatString(this string format, params object[] args)
{
    return string.Format(format, args);
}

// usage
string message = "Welcome {0} (Last login: {1})".FormatString(userName, lastLogin);

IsNull

public static bool IsNull(this object source)
{
    return source == null;
}

// usage
public void ProcessData(DataSet input)
{
    if (!input.IsNull())
    {
        // business logic here
    }
}

Links

Multipurpose extension methods
http://www.extensionmethod.net/csharp/object

NullSafe

public static TResult NullSafe<TObj, TResult>(
	this TObj obj, 
	Func<TObj, TResult> func, 
	TResult ifNullReturn = default(TResult))
{
	return obj != null ? func(obj) : ifNullReturn;
}

// usage
foo.NullSafe(f => f.GetBar())
   .NullSafe(b => b.Baz)
   .NullSafe(b => b.SomeMethod(), ifNullReturn: "whatever you would return in the null case");

ThrowIf

public static class Throw<TException> where TException : Exception
{
    public static void If(bool condition, string message) 
    {
        if (condition)
        {
            throw (TException)Activator.CreateInstance(typeof(TException), 
                                                       message);
        }
    }
}

Traverse

public static class Traverse
{
    public static IEnumerable<T> Along<T>(T node, Func<T, T> next) 
            where T : class
    {
        for (var current = node; current != null; current = next(current))
        {
            yield return current;
        }
    }
}

// usage
catch (Exception ex)
{
    var sqlException = Traverse.Along(ex, e => e.InnerException)
                               .OfType<SqlException>()
                               .FirstOrDefault();
}