Any hardcore Excel C API XLL developers on the forum? I have a question or two about using the internal Excel data types, the XLOPERs, as XLL function arguments. The 2013 MS XLL SDK sample code (latest version) uses the U data registration type (XLOPER12) for XLL function arguments, and “coerces” them using the xlCoerce function call (embedded within the omnibus Excel12 callback function) to test whether function arguments are of the expected data type before any calculations are effected.
Is xltypeMulti strictly reserved for coerced variables? That is, can they only be created using xlCoerce or can one somehow read an xltypeMulti as a XLL function argument? What does one have to pass as an argument to the Excel Function Wizard for an XLL argument to evaluate as xltypeMulti? Does Steve Dalton's textbook on add-in development address this?
Oh, being pretty old school when it comes to software, I am not interested in 3rd party tools to manage this stuff. I prefer to go straight to the source, which in this case is a bit thinly documented.