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Does dot net have an interface like IEnumerable with a count property? I know about interfaces such as IList and ICollection which do offer a Count property but it seems like these interfaces were designed for mutable data structures first and use as a read only interface seems like an afterthought - the presence of an IsReadOnly field and mutators throwing exceptions when this property is true is IMO ample evidence for this.
For the time being I am using a custom interface called IReadOnlyCollection (see my own answer to this post) but I would be glad to know of other alternative approaches.
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IEnumerable has not Count function or property. To get this, you can store count variable (with foreach, for example) or solve using Linq to get count.
IEnumerable is an interface defining a single method GetEnumerator() that returns an IEnumerator interface. It is the base interface for all non-generic collections that can be enumerated. This works for read-only access to a collection that implements that IEnumerable can be used with a foreach statement.
Like a class, Interface can have methods, properties, events, and indexers as its members. But interfaces will contain only the declaration of the members. The implementation of the interface's members will be given by class who implements the interface implicitly or explicitly.
An interface may define a default implementation for members, including properties. Defining a default implementation for a property in an interface is rare because interfaces may not define instance data fields.
The key difference between the ICollection family and the IEnumerable family is the absence of certainty as to the count of items present (quite often the items will be generated/loaded/hydrated as needed) - in some cases, an Enumerable may not ever finish generating results, which is why the Count is missing.
Deriving and adding a Count is possible depending on your requirements, but it goes against this spirit, which is the purpose of ICollection - a collection of stuff that's all there.
Another way might be to use the System.Linq.Enumerable.Count method, i.e.
using System.Linq;
class X
{
void Y(IEnumerable<int> collection)
{
int itemCount = collection.Count();
}
}
or use the (System.Linq.Enumerable) .ToList() to pull all the items from the enumerator into a Collection and work from there.
(Also to answer your comment before having 50 rep:- the ".Count()" bit is a call to an extension method on the extension class System.Linq.Enumerable - the extension method is available on all things that derive from IEnumerable because the code has a "using System.Linq" which brings the extension methods in all classes in that namespace into scope - in this case its in the class Enumerable. If you're in VS, pressing F12 will bring you to the definition of S.L.Enumerable. BTW C# In Depth is a fantastic book for learning LINQ properly - its a page turner thats really helps you get the whole picture compared to learning the bits of LINQ piece by piece)
132
As of .Net 4.5, there are two new interfaces for this: IReadOnlyCollection<T> and IReadOnlyList<T>.
IReadOnlyCollection<T> is IEnumerable<T> with a Count property added, IReadOnlyList<T> also adds indexing.
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