How do I implement structural Equals for an F# class?

Question

In C# I would implement Equals for a class with structural equality like this:

public override bool Equals(object obj)
{
    if (this == obj)
    {
        return true;
    }

    var other = obj as MyType;
    if (other != null)
    {
        return someField == other.someField && 
            someOtherField == other.someOtherField;
    }

    return false;
}

In F# we have records for this, but if we want to use inheritance a type must be implemented.

What is the equivalent Equals implementation in F#?

Answer 1

As mentioned in the comments, you just need to override Equals. The compiler will also tell you that it is a good idea to override GetHashCode.

One neat trick is that you can just take all the relevant fields of your class, create tuples with them and then compare the tuples (or take hash code of the tuple). This makes the implementation much easier than if you were doing this by hand:

type Person(name:string, age:int) =
  member x.Name = name
  member x.Age = age
  override x.GetHashCode() =
    hash (name, age)
  override x.Equals(b) =
    match b with
    | :? Person as p -> (name, age) = (p.Name, p.Age)
    | _ -> false

Person("Joe", 42) = Person("Joe", 42)