So you need to be mindful and have intelligent overloads for the DoSomething method?

Personally, I don't really see that as much of a problem. Having run into that issue before, I think the compiler catches it as as an error because its an ambiguous method signature. Instead, you have to pass something like: "DoSomething("foo", (string)null)" which, in that case, defeats the purpose of the optional parameter altogether.

Yeah, been through that before. We just standardised on using overloads for external APIs, it's cleaner externally.

The real issue is if you have DoSomething(string what, autoRetry=true) and you change to DoSomething(string what, autoRetry=false) - DLLs compiled against the old version will call with true even if the authors wanted the default behaviour.

That makes sense. As I said in my other thread, I locally deal with that problem by passing null instead of a primitive (though admittedly, I would probably use a primitive in cases of bool).

That said, in this circumstance my method sounds more like a hack and yours the cleaner, correct route.