Question

Understanding IEnumerable Interface

Asked by: Programmer_to_be

Dear experts,
I am having some trouble understanding the use of the generic IEnumerable interface. When I implement this interface in one of my collection classes, the compiler requires me to implement two methods, these are:-

public IEnumerator<SomeType> GetEnumerator();
and:-
IEnumerator IEnumerable.GetEnumerator();

By using the yield keyword I can understand the use of the first GetEnumerator method... but why is the second GetEnumerator method required? In that method I'm just forced to call the first enumerator method and Its access is private so what use does this method have? Could someone explain its purpose for being there?

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Asked On
2007-06-11 at 18:23:22ID22627447
Tags

generic

,

interface

,

understanding

Topics

C# Programming Language

,

.NET

,

.NET Framework 2.x

Participating Experts
2
Points
125
Comments
3

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Answers

 

by: crazycomputersPosted on 2007-06-11 at 19:23:14ID: 19263247

The use is that by implementing both IEnumerable`1 (the generic interface) and IEnumerable, the object can be used by APIs that need an IEnumerable instance.  It's more for backwards compatibility.

Note that using an explicit interface implementation (IEnumerator IEnumerable.GetEnumerator()) as opposed to implicit (public IEnumerator GetEnumerator())  does make the method private, but it can still be accessed by casting to IEnumerable:

((IEnumerable) this).GetEnumerator();

For example.

 

by: cheddar73Posted on 2007-06-11 at 20:18:24ID: 19263417

Excellent answer by crazycomputers.

Just thought I'd add that the reason the compiler complains when you don't include the second GetEnumerator() method is that the IEnumerable<T> generic interface itself inherits the IEnumerable non-generic interface.  When you implement an interface you must also implement any interface that interface inherits.  Both of these interfaces declare a GetEnumerator() method.  That means it is necessary to provide an implementation of IEnumerable<T>.GetEnumerator() *as well as* IEnumerable.GetEnumerator() whenever you implement IEnumerable<T>.

 

by: Programmer_to_bePosted on 2007-06-12 at 03:31:19ID: 19264839

thanks, that makes much more sense now.

20120131-EE-VQP-002

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