What’s the difference between IEquatable and just overriding Object.Equals()?

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The main reason is performance. When generics were introduced in .NET 2.0 they were able to add a bunch of neat classes such as List<T>, Dictionary<K,V>, HashSet<T>, etc. These structures make heavy use of GetHashCode and Equals. But for value types this required boxing. IEquatable<T> lets a structure implement a strongly typed Equals method so no boxing is required. Thus much better performance when using value types with generic collections.

Reference types don’t benefit as much but the IEquatable<T> implementation does let you avoid a cast from System.Object which can make a difference if it’s called frequently.

As noted on Jared Parson’s blog though, you must still implement the standard Object.Equals and Object.GetHashcode overrides.

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