Should type be of type Type? (31 Dec 2005)

The other day, we were writing some .NET code for which we produced COM wrappers, including a type library (through tlbexp). One of the exported methods looked like this (in Managed C++):

  void AddButton(String *title, String *icon, ActionType type);

In a COM test client which referred to said type library, the compiler reported inexplicable errors. They hinted that the parameter named (!) type somehow was thought to be of type System.Type... but why? type is correctly declared as an ActionType, not as System::Type!

I won't tell you what other means we used to track down this issue; let me just advise you to clean those chicken blood stains as early as possible, before they stick to your keyboard just like, well, chicken blood .-) In the end, Adam Nathan's blue bible had the right hint for us: Type libraries maintain a case-insensitive identifier table. Once an identifier has been added to the table in one case, any subsequent attempts to add the identifier to the table again will simply fail, regardless of the case.

So in our example, the first "type"-ish identifier which was added to the table was System::Type. (Or maybe it was actually a parameter called type which was of type System::Type?). Later, the parameter name type was encountered, but no longer added to the table because of its unlikely relative which made it into the table first. Any subsequent references to anything called "type" or "Type" or "tYPE" would then resolve to System::Type, with the aforementioned consequences.

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