LexParse

If you’ve used LINQ and lambdas, I’m sure you’ve come across the occasional function that requires an implementation of IEqualityComparer,or IComparer. You were hoping to write a little Lambda predicate but NOOOOOO, now you have to create a new type and implement an interface. Well no longer. I’m hoping these are the last two classes, in the history of mankind, that inherit from IComparer and IEqualityComparer:

public class Comparer<T> : IComparer<T>
{
   private Func<T, T, int> _compareFn;

   public Comparer(Func<T, T, int> fn)
   {
      _compareFn = fn;
   }

   public int Compare(T x, T y)
   {
      return _compareFn(x, y);
   }

}

public class EqualityComparer<T> : IEqualityComparer<T>
{
   private Func<T, T, bool> _equalsFn;
   private Func<T, int> _getHashCodefn;

   public EqualityComparer(Func<T, T, bool> equalsFn, Func<T, int> getHashCodefn)
   {
      _equalsFn = equalsFn;
      _getHashCodefn = getHashCodefn;
   }

   public bool Equals(T x, T y)
   {
      return _equalsFn(x, y);
   }

   public int GetHashCode(T obj)
   {
      return _getHashCodefn(obj);
   }
}

2 Examples:

List<int> l = new List<int> { 1, 2, 5, 7, 999, 234, 4 };
l.Sort(new Comparer<int>((x, y) => x < y ? -1 : x == y ? 0 : 1));

Dictionary<int, string> d = new Dictionary<int, string>() { { 1, "a" }, { 2, "a" }, { 3, "b" } };

var d2 = d.Distinct(new EqualityComparer<KeyValuePair<int, string>>(
   (kvp1, kvp2) => kvp1.Value == kvp2.Value, kvp => kvp.Value.GetHashCode()));