Object Comparison in .net

Question

Is it any different from the CLR standpoint to implement IEqualityComparer vs overriding the == operator for the property you would use in the IEqualityComparer<T>? And if so, when would you use one against the other?

Edit

Ok it does make sense that the IEqaulityComparer used by the implementations of Hashtable - it slipped out of my mind when I was posting the question. So what about the extensions of Linq of IEnumerable. Does that mean that .net builds up a Hashtable when executing those kind of extension methods?

Answer 1

IEqualityComparer is not equal, equal is for object (instance method) but EqualityComparer is for decoration for example in linq you want do specific distinct:

personList.OrderBy(p=>p.ID).Distinct(new MyEqualityComparer())

and

  class MyEqualityComparer: IEqualityComparer<Person>
  {

    public bool Equals(Person p1, Person p2)
    {
       if (p1.Age == p2.Age)
          return true;
       return false;
    }


    public int GetHashCode(Person p)
    {
        return p.Id.GetHashCode();
    }

  }

but equal is for Person:

public class Person
{
 public int ID{get;set;}
 public int Age{get;set;}
 public override bool Equals(object o)
 {
   //do stuff
 }
}

you can do any number of decoration by IEqualityComparer but you can't do this by instance method (you can write personList.Distinct(new AnotherComparer) ,...)