What's wrong with defining operator == but not defining Equals() or GetHashCode()?

Question

For the code below

public struct Person
{
    public int ID;
    public static bool operator ==(Person a, Person b) { return  a.Equals(b); }
    public stati         


        

Answer 1

My guess is your are getting these warning because compiler doesn't know that you use Equals in == method

Suppose you have this implementation

public struct  Person
{
    public int ID;
    public static bool operator ==(Person a, Person b) { return Math.Abs(a.ID - b.ID) <= 5; }
    public static bool operator !=(Person a, Person b) { return Math.Abs(a.ID - b.ID) > 5; }
}

Then

 Person p1 = new Person() { ID = 1 };
 Person p2 = new Person() { ID = 4 };

 bool b1 = p1 == p2;
 bool b2 = p1.Equals(p2);

b1 would be true, but b2 false

--EDIT--

Now suppose you want to do this

Dictionary dict = new Dictionary();
dict.Add(p1, p1);
var x1 = dict[p2]; //Since p2 is supposed to be equal to p1 (according to `==`), this should return p1

But this would throw an exception something like KeyNotFound

But if you add

public override bool Equals(object obj)
{
    return Math.Abs(ID - ((Person)obj).ID) <= 5; 
}
public override int GetHashCode()
{
    return 0;
}

you will get what you want.

The compiler just warns you that you can face with similar conditions