What is the minimum interface that has the Count property in .Net

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+4 Q:

What is the minimum interface that has the Count property in .Net

Hello,

I need to change a method that has one parameter that takes a serie of objects. I need to find the lowest Interface (in inheritance tree) that has the Count property. Until now I was using the IEnumerable but as this has not Count I need to change it to the wider interface possible so the method can work with the biggest number of types of series (collections, lists, arrays, etc).

Thanks in advance.

+6 A:

ICollection adds the Count property.

As @Joren rightly points point, IEnumerable<T> has the extension method Count<T>() if you're happy making your collection generic. However, as @Joel Coehoorn has pointed out, it is inadvisable to use this as it forces an iteration of the sequence.

David Neale 2010-05-21 07:43:54

That's the lowest at the Hierarchy tree?

SoMoS 2010-05-21 07:48:14

The Count<T> method is an extension method on IEnumerable<T>, not a method on ICollection<T>. (ICollection<T> just has the Count property, which it inherits from ICollection.) Of course ICollection<T> inherits from IEnumerable<T>, so the extension method is valid on ICollection<T> instances. My point is that for the Count<T> method, IEnumerable<T> is more fundamental than ICollection<T>.

Joren 2010-05-21 07:49:37

Ah, thanks @Joren. I'll amend the answer.

David Neale 2010-05-21 08:03:01

Yes, ICollection is what adds the Count property. Other things that have the property will generally be implementing ICollection (IList, IDictionary etc.).

David Neale 2010-05-21 08:48:46

Don't use IEnumerable's .Count extension. It forces an iteration of the sequence.

Joel Coehoorn 2010-05-24 15:46:05

Thanks for pointing that out - answer amended.

David Neale 2010-05-24 15:53:22

+4 A:

ICollection adds the Count property.

Dean Harding 2010-05-21 07:44:35

+3 A:

System.Collections.ICollection, and also System.Collections.Generic.ICollection<T>. These two interfaces have no relation to eachother, but both inherit from IEnumerable, so they're at the same level.

IEnumerable obviously does not have a Count property (the count isn't necessarily predetermined).

Thorarin 2010-05-21 07:44:59

ansaurus

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What is the minimum interface that has the Count property in .Net

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