What’s in a name? (C#’s hidden support for structural typing) (opens in new tab)

I suspect the reason this works this way is because `foreach` is a language construct - not a part of the .NET Framework Class Library. On the other hand, `IEnumerable` is an interface defined in the class library that ships as part of the .NET runtime. Having the foreach construct require implementing IEnumerable will tie the compiler to a specific class definition. So instead, it only looks for a method with that name, which happens to be formalized in the class library in the form of an interface called IEnumerable.

Edit: hm.. but I note that this doesn't work for the using(){} construct.

This requires the object to implement an interface that is convertable to IDisposable instead of just looking for a `Dispose` method.

I always found this somewhat inelegant. I suppose given all the constraints, its OK, but it feels like such a feature (such as the collection initializers) should be based on language constructs, not compiler special cases.

How can I use this structural typing feature?

AOP weavers like postsharp let you do some duck typing like stuff by injecting interfaces as post compile step.

The big one he doesn't cover is LINQ query syntax. There's a post on my blog ( http://contextfree.livejournal.com ) where I explain why it works this way ...