Question

I have a collection class MyCollection<T>.

I have implemented T this[string name], which works fine.

I tried to also implement T Item(string name) but of course that gave an error:

The type MyCollection<T> already contains a definition for Item

as it should. However I also want to overload Item by implementing a function T Item(string, bool) but this also throws up the same error.

Why would the compiler think that T Item(string, bool) clashes with the indexer T Item(string)? If it weren’t an indexer but just an ordinary method these two declarations would be two perfectly valid overloads.

Answer 1

You can absolutely overload an indexer – but you can’t overload it with a method called Item. To overload the indexer, you just need:

public T this[string name, bool condition]
{
    get { ... }
    set { ... }
}

EDIT: Okay, so it looks like:

• You can’t have two members of different kinds (one method, one property) with the same name, which is correct according to section 10.3 of the C# 4 spec
• You can’t have an indexer and a property of name Item, which is slightly surprising as they’re both properties under the hood

I suspect that you can have indexers alongside properties called Item if you change the generated name of the indexer’s property using DefaultMemberAttribute, but I haven’t tried it.