"eramf***@gmail.com" wrote:

> Why doesnt ArrayList implements the Equals() or GetHashCode() methods?
> How is the developer supposed to check if an array list is equal to
> another array list? Is the developer supposed to iterate through the
> array list to find out if they are equal or not? This should be handled
> by the framework classes and I don't want to do any unnecessary
> implementation (read copy-paste-problems).
>
> If I look through the other classes in System.Collection I see that no
> implements GetHashCode() or Equals(). If none of them do, then it must
> be a design choice. But what design choice would that be? If anyone
> have any explanation, please let me know.I really want to know.
>
> There is an interface in System.Collections.Generic that is named
> IEqualityComparer, which has two methods, Equals() and GetHashCode().
> Why make an interface when every class implements those methods? And
> why doesn't the default list/collection classes implement this
> interface?
>
> <flamebait-to-be-ignored>
> If I look to Java, the ArrayList implements equals(), hashCode() as all
> good objects should. They have also a good explanation on how it is
> done here.
> http://shorl.com/gogedrikekati
> http://shorl.com/fygafrebrypeko
> </flamebait-to-be-ignored>
>
> Sorry that this post was double posted into the usenet aspnet group.
>
> Regards
> http://redsolo.blogspot.com
>
>

"eramf***@gmail.com" wrote:

> Ciaran O''Donnell skrev:
> > What would the arraylist return for GetHashCode, would it aggregate the
> > hascodes of your classes. As for equals, would you have it check to see if
> > all of the elements are equal, should they be equal in reference or in value,
> > and does that make the arraylist equal or is it equal if it points to the
> > same actual arraylist. The last one is the one the COR team chose and if you
> > want to have a difference meaning for equals then you should implement it.
>
> If you check the two links my original post contained, you can read
> another approach to this. They would aggregate the hashcodes of the
> contained objects and return that. That way you can have two lists
> generate the same hashcode if they contains "equal" objects. Which I
> needed as I had two array lists at the server and client, and the
> simplest way to check if they were equal would be by using the
> GetHashCode().
>
> For equality, it is very simple. The list should go through the
> contained objects and check if they are "equal". Now it is up to the
> contained class/objects to define "equality". The objects/classes can
> define if they should be equal in value or in reference. That way the
> framework gives the option to the developer to implement Equals() or
> not. But unfortunately this decision is already made for the developer.
>
> The default equals method is to check if the two object references are
> the same. That is exactly similar to the "obj1 == obj2" statement. In
> my view all good classes should implement Equals() (and therefore
> GetHashCode()), so the user of a class can make a choice in either
> check for reference equality OR value equality.
>
> > In .NET 2, the list has the True for all predicate which you could pass an
> > anonymous method to to compare is to the first element, this would be like
> > the equals you are after but in a short bit of code.
>
> Yes, that would be less code. But it would be much less code if the
> Collection classes implemented Equals(). Right?
>
> It is a nice feature that developers can easily change the equality
> meaning, but I havent done so in a real project yet.
>
> //E
>
>