C# .NET Interface implementation at multiple levels

Question

I found myself digging into System.Collections.Generic when using a BindingList. I don't understand something about the following interface implementations:

public interface ICollection<T> : IEnumerable<T>, IEnumerable
public interface ISet<T> : ICollection<T>, IEnumerable<T>, IEnumerable

Why does

ISet<T>

Implement

IEnumerable<T>, IEnumerable

when ICollection already does? Wouldn't the following be acceptable?

public interface ICollection<T> : IEnumerable<T>, IEnumerable
public interface ISet<T> : ICollection<T>

Any help understanding this is much appreciated. Thanks!

What source are you looking at? referencesource.microsoft.com/#System/compmod/system/… — Dan Wilson
– Dan Wilson, Commented May 1, 2018 at 13:37
Look at the source code: referencesource.microsoft.com/#System/compmod/system/… - It's just Visual Studio that's showing you all interfaces in the hierarchy — haim770
– haim770, Commented May 1, 2018 at 13:38
Microsoft likes repeating inherited interface declarations, it is excellent self-documentation. It makes no difference whatsoever to the code or the runtime behavior. — Hans Passant
– Hans Passant, Commented May 1, 2018 at 13:42
Thanks @HansPassant, your comment was the nice, concise answer I was really looking for. — Jacob Peterson
– Jacob Peterson, Commented May 1, 2018 at 14:36

marc_s · Accepted Answer · 2021-04-11 06:51:21Z

2

I assume you have the interface declarations from MSDN or another documentation source. While it is right that ISet<T> does not have to explicitly implement IEnumerable<T> and IEnumerable as you can see in the reference implementation ...

public interface ISet<T> : ICollection<T>

... documentations still contain the complete list as a convenience for the developer so they know what interfaces are implemented by ISet<T> even if only through inheritance. Going through a possibly long inheritance hierarchy would probably not enhance the benefit of such a documentation.

edited Apr 11, 2021 at 6:51

marc_s

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answered May 1, 2018 at 13:39

adjan

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1 Comment

Jacob Peterson Over a year ago

I figured this was a convenience/readability feature but thought I'd ask the community. Thanks @Adrian!

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