#1,142 – Using EqualityComparer to Compare Objects in Generic Types

By default, you can’t use equality operators on objects whose type is a type argument within a generic class.  If you constrain an argument to be a reference type, you can use equality operators to do reference equality checks.  But you can‘t make use of overloaded equality functionality.

You can do a true equality check between objects using the EqualityComparer<T> class.  Below is an example.  EqualityComparer<T> makes use of overloaded equality logic in the Dog class, even though we haven’t constrained the T argument.

    public class Pile<T>
    {
        List<T> pile = new List<T>();
        EqualityComparer<T> comparer = EqualityComparer<T>.Default;

        public void Add(T item)
        {
            if (!pile.Contains(item))
                pile.Add(item);
        }

        public bool IsFirst(T item)
        {
            // Reference equality only, if we do
            //   where T : class
            //bool equalStd = (pile[0] == item);

            // Makes use of overloaded Equality
            // functionality in T
            bool equalBetter = comparer.Equals(pile[0], item);

            return equalBetter;
        }
    }

1142-001

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About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

2 Responses to #1,142 – Using EqualityComparer to Compare Objects in Generic Types

  1. Pingback: Dew Drop – July 21, 2014 (#1818) | Morning Dew

  2. Pingback: Tools Of The Trade - The Daily Six Pack: July 22, 2014

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