#1,143 – Implement IEquatable in a Generic Type

You can use the EqualityComparer<T> type to implement IEquatable<T> for a generic type.

In the example below, we implement IEquatable<TwoThings<T1,T2>> for our TwoThings<T1,T2> type.  The EqualityComparer<T> type is used to properly compare member data, regardless of the types.  Without this, the compiler wouldn’t know how to compare two T1 or two T2 objects.

    public class TwoThings<T1,T2> : IEquatable<TwoThings<T1,T2>>
    {
        T1 thing1;
        T2 thing2;

        EqualityComparer<T1> comparer1 = EqualityComparer<T1>.Default;
        EqualityComparer<T2> comparer2 = EqualityComparer<T2>.Default;

        public TwoThings(T1 thing1, T2 thing2)
        {
            this.thing1 = thing1;
            this.thing2 = thing2;
        }

        // IEquatable
        public bool Equals(TwoThings<T1, T2> other)
        {
            return (comparer1.Equals(thing1, other.thing1) &&
                    comparer2.Equals(thing2, other.thing2));
        }
    }

Now suppose that we construct this class using types that implement value equality.  The Equals method then behaves as we’d expect.

            Dog myDog = new Dog("Jack", 5);
            TwoThings<Dog, string> first = new TwoThings<Dog, string>(myDog, "Feisty");

            Dog otherDog = new Dog("Jack", 5);
            TwoThings<Dog, string> second = new TwoThings<Dog, string>(otherDog, "Feisty");

            // Returns true
            bool eq = first.Equals(second);
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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.

One Response to #1,143 – Implement IEquatable in a Generic Type

  1. Pingback: Dew Drop – July 22, 2014 (#1819) | Morning Dew

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