New Collection interfaces in C# 3.0

Question

What are the new collection interfaces available in C# 3.0 ?

In C# 2.0

IComparer

IEqualityComparer

IEnumerator

IEnumerable

ICollection

IDictionary

IDictionaryEnumerator

IList.

Answer 1

.NET 3.5 (commonly confused with C# 3.0, although they are completely separate) introduced:

• IGrouping<TKey,TValue>
• ILookup<TKey,TValue>
• IOrderedEnumerable<T>
• IOrderedQueryable
• IOrderedQueryable<T>
• IQueryable
• IQueryable<T>
• IQueryProvider

and concrete types:

• HashSet<T>
• Lookup<TKey,TValue>

(and a load of private stuff, but those are the main public ones)

Answer 2

No new interfaces AFAIK, but in the .NET Framework 3.5 (C# 3) you get the new HashSet<T> collection class which implements a set (in the System.Core assembly).

Answer 3

(Collection) interfaces are defined in the .Net class libraries, not in the C# language.

And in .Net 2.0 your list is missing all the generic interfaces. In .Net 3.0 there weren't any new.

Answer 4

You can compare collection interfaces available in C# 2.0 with collection interfaces available in C# 3.0

no new interface.

Answer 5

As far as I can tell, there's nothing new in 3.0 when it comes to collection interface.

.NET 3.0 (not just C#) have new Collection Initializers:

List<Class1> someClasses = new List<Class1>
         {
            new Class1
            {
               Prop1 = "abc",
               Prop2 = 123
            },
            new Class1
            {
               Prop1 = "xyz",
               Prop2 = 789
            }
         };