Why doesn't ICollection<T> implement ICollection?
This question already has an answer here:
As Nick said, ICollection is pretty much useless.
These interfaces are similar only by their name, CopyTo and Count are the only properties in common. Add , Remove , Clear , Contains and IsReadOnly have been added while IsSychronized and SyncRoot have been removed.
In essence, ICollection<T> is mutable, ICollection is not.
Krzysztof Cwalina has more on this topic
ICollection<T> seems like ICollection , but it's actually a very different abstraction. We found that ICollection was not very useful. At the same time, we did not have an abstraction that represented an read/write non-indexed collection. ICollection<T> is such abstraction and you could say that ICollection does not have an exact corresponding peer in the generic world; IEnumerable<T> is the closest.
ICollection<T> and ICollection are actually very different interfaces that unfortunately share a name and not much else.
From http://blogs.msdn.com/b/kcwalina/archive/2005/09/23/collections.aspx
ICollection<T> seems like ICollection , but it's actually a very different abstraction. We found that ICollection was not very useful. At the same time, we did not have an abstraction that represented an read/write non-indexed collection. ICollection<T> is such abstraction and you could say that ICollection does not have an exact corresponding peer in the generic world; IEnumerable<T> is the closest.
First, IList<T> does not implement IList either, probably for the same reasons. IList<T> implements: ICollection<T>, IEnumerable<T>, IEnumerable
Some parts of ICollection just aren't necessary, but changing an interface after it's out in the wild is breaking at best.
Look at ICollection:
public interface ICollection : IEnumerable
{
void CopyTo(Array array, int index);
int Count { get; }
bool IsSynchronized { get; }
object SyncRoot { get; }
}
It's just not properties you need in most cases, when I want a Collection I've never once needed this, nor would want to implement it. It got old would be the reasoning I suppose, but you'd have to ask the .Net team for the affirmative answer.
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