Claus Brod: Should <tt>type</tt> be of type Type? (31 Dec 2005)

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---+++ [[BlogOnSoftware20051231Type][Should <tt>type</tt> 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++):
<verbatim>
  void AddButton(String *title, String *icon, ActionType type);
</verbatim>

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 [[http://msdn.microsoft.com/library/en-us/cpref/html/frlrfsystemtypeclasstopic.asp][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, [[http://search.barnesandnoble.com/bookSearch/isbnInquiry.asp?sourceid=00387042536162273707&ISBN=067232170X&bfdate=01-21-2005+15:54:04][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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