Question

public class MyClass
{
    public string myString;

    public MyClass(string s)
    {
        this.myString = s;
    }
}

In IEnumerable<MyClass> how can I change the default value of FirstOrDefault() method
For example I want to return new MyClass("HelloWorld");

Edit: Is there a way to override default value of a Class?
Like Default Value of MyClass is new MyClass("Default");

Answer 1

You can’t directly change it. But you have a few alternatives.

If your sequence contains no nulls you can use:

MyClass result = seq.FirstOrDefault() ?? new MyClass("HelloWorld");

Or you can implement your own version which takes a parameter for the default value:

    public static T FirstOrDefault<T>(this IEnumerable<T> source, T defaultValue)
    {
        using (IEnumerator<T> enumerator = source.GetEnumerator())
        {
            if (enumerator.MoveNext())
                return enumerator.Current;
            else
                return defaultValue;
        }
    }

    public static T FirstOrDefault<T>(this IEnumerable<T> source, Func<T, bool> predicate, T defaultValue)
    {
        using (IEnumerator<T> enumerator = source.Where(predicate).GetEnumerator())
        {
            if (enumerator.MoveNext())
                return enumerator.Current;
            else
                return defaultValue;
        }
    }

You could also use a different name for your this implementation of FirstOrDefault, but since it doesn’t collide with any of the existing overloads, I just used the same name.

https://github.com/CodesInChaos/ChaosUtil/blob/master/Chaos.Util/LinqExtensions.cs