1.9.1.2 Out parameters

For out parameters,

• If nil is passed, the value from the method is returned without any conversion.
• For a parameter whose type is an array type or a pointer type with a size_is attribute, the value can be a Lisp array. The contents of the array will be modified by the method and the array will be returned as a value.
• Otherwise, the value should be a foreign pointer of the type that the FLI would generate for the parameter's type. The foreign pointer will be returned as a value.

LispWorks COM/Automation User Guide and Reference Manual - 19 Dec 2011