Overload resolution priority on extension methods

[jhudsoncedaron]

This one is actually ambiguous in the specification at https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-13.0/overload-resolution-priority ; the problem is there is not one specification for the whole language so it depends on which order you read specification components.

Anyway this problem has been a thorn in our side for awhile; There's an extension method on IDictionary<,> called GetValueOrDefault() which is convenient; and we added another IReadOnlyDictionary<,> called GetValueOrDefault() for the same reason the the stock one was added. Guess what happens when someone tries to call Dictionary.GetValueOrDefault()

When I read the specification for overload resolution priority https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-13.0/overload-resolution-priority ; unless I read it in the mode of how can the specification be twisted to make the most trouble possible, I conclude placing [OverloadResolutionPriority(-1)] on my method should mask it and allow Dictionary<,>.GetValueOrDefault() to resolve to the stock one.

I can't rule out the possibility that we were there first and Microsoft is the one who added the colliding name. I am not the one who made this method.

Sample project is attached. In the production version it wouldn't matter which function is called.
x.zip

[colejohnson66]

OverloadResolutionPriority only applies to members within the same type. It does not solve ambiguity arising from multiple matching extension methods.

[jhudsoncedaron]

That's what the implementation does. The spec is ambiguous.

[333fred]

No, the spec is not ambiguous.

Then, the reduced set of candidate members is grouped by declaring type. Within each group: (lists the rules of orpa)

There's further an explicit question on this: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-13.0/overload-resolution-priority#open-questions