Using lambda expression in place of IComparer argument

Question

Is it possible with C# to pass a lambda expression as an IComparer argument in a method call?

eg something like

var x = someIEnumerable.OrderBy(aClas         


        

Answer 1

If you consistently want to compare projected keys (such as a single property), you can define a class that encapsulates all the key comparison logic for you, including null checks, key extraction on both objects, and key comparison using the specified or default inner comparer:

public class KeyComparer : Comparer
{
    private readonly Func _keySelector;
    private readonly IComparer _innerComparer;

    public KeyComparer(
        Func keySelector, 
        IComparer innerComparer = null)
    {
        _keySelector = keySelector;
        _innerComparer = innerComparer ?? Comparer.Default;
    }

    public override int Compare(TSource x, TSource y)
    {
        if (object.ReferenceEquals(x, y))
            return 0;
        if (x == null)
            return -1;
        if (y == null)
            return 1;

        TKey xKey = _keySelector(x);
        TKey yKey = _keySelector(y);
        return _innerComparer.Compare(xKey, yKey);
    }
}

For convenience, a factory method:

public static class KeyComparer
{
    public static KeyComparer Create(
        Func keySelector, 
        IComparer innerComparer = null)
    {
        return new KeyComparer(keySelector, innerComparer);
    }
}

You could then use this like so:

var sortedSet = new SortedSet(KeyComparer.Create((MyClass o) => o.MyProperty));

You can refer to my blog post for an expanded discussion of this implementation.