Question

I know the importance of overriding GetHashCode when implementing custom equality checks – for which I have implemented IEquality<T> interface, and also the difference between generic and non-generic Equals as discussed here. Now is there a point to override Equals(object t)? Wouldn’t everything come under generic Equals(T t)?

public override int GetHashCode() //required for hashsets and dictionaries
{
    return Id;
}

public bool Equals(T other) //IEquatable<T> here
{
    return Id == other.Id;
}

public override bool Equals(object obj) //required??
{
    return Equals(obj as T);
}

Answer 1

From msdn:

If you implement IEquatable, you should also override the base
class implementations of Object.Equals(Object) and GetHashCode so that
their behavior is consistent with that of the IEquatable.Equals
method. If you do override Object.Equals(Object), your overridden
implementation is also called in calls to the static
Equals(System.Object, System.Object) method on your class. In
addition, you should overload the op_Equality and op_Inequality
operators. This ensures that all tests for equality return consistent
results.

I could have done a better google search too. Here’s a good article on msdn blogs by JaredPar on the subject.

In short, overriding Equals(object obj):

Needed for the static Equals(object obj1, object obj2) method on object class, or for Contains(object item) on ArrayList instance etc..

Accepting this since the link is more thorough on the subject. Thanks to Oded too..