add COM enumeration support

pkgs/racket-doc/scribblings/foreign/com-auto.scrbl

@@ -352,6 +352,29 @@ Racket. (The DLL is the same for all Racket versions.)}
 Removes any existing callback for @racket[name] in @racket[obj].}
 
 
+@; ----------------------------------------
+
+@section{COM Enumerations}
+
+@defproc[(com-enumerate-to-list [obj com-object?]) list?]{
+
+Produces the elements that @racket[obj] would generate as the
+driver of a for-each loop in Visual Basic or PowerShell.
+
+A call @racket[(com-enumerate-to-list obj)] is equivalent to
+@racket[(com-enumeration-to-list (com-get-property obj "_NewEnum"))].
+
+@history[#:added "6.2.0.2"]}
+
+
+@defproc[(com-enumeration-to-list [obj com-object?]) list?]{
+
+Given a COM object that implements @cpp{IEnumVARIANT}, extracts the
+enumerated values into a list.
+
+@history[#:added "6.2.0.2"]}
+
+
 @; ----------------------------------------
 
 @section{Interface Pointers}
@@ -381,7 +404,6 @@ interface} extends @cpp{IUnknown}, so @racket[com-iunknown?] returns
 Returns @racket[#t] if @racket[v] corresponds to an unsafe
 @cpp{IDispatch}, @racket[#f] otherwise.}
 
-
 @; ----------------------------------------
 
 @section[#:tag "remote"]{Remote COM servers (DCOM)}

racket/collects/ffi/com.rkt

@@ -24,6 +24,9 @@
          com-unregister-event-callback
          com-make-event-executor com-event-executor?
 
+         com-enumeration-to-list
+         com-enumerate-to-list
+
          com-object-get-iunknown com-iunknown?
          com-object-get-idispatch com-idispatch?
 

racket/collects/ffi/unsafe/com.rkt

@@ -61,6 +61,9 @@
          com-register-event-callback
          com-unregister-event-callback
 
+         com-enumeration-to-list
+         com-enumerate-to-list
+
          com-object-get-iunknown com-iunknown?
          com-object-get-idispatch com-idispatch?
 
@@ -2276,6 +2279,40 @@
 (define (com-iunknown? v) (and (IUnknown? v) #t))
 (define (com-idispatch? v) (and (IDispatch? v) #t))
 
+;; ----------------------------------------
+;; Enumerations
+
+(define IID_IEnumVARIANT
+  (string->guid "{00020404-0000-0000-c000-000000000046}"))
+
+(define-com-interface (_IEnumVARIANT _IUnknown)
+  ([Next (_mfun (_ulong = 1)
+		(els : (_ptr o _VARIANT))
+		(got : (_ptr o _ulong))
+		 -> (r : _HRESULT)
+		 -> (if (= got 1)
+			els
+			#f))]
+   ;; ... more methods ...
+   ))
+
+(define (com-enumeration-to-list obj)
+  (define i
+    (QueryInterface (com-object-get-iunknown obj)
+		    IID_IEnumVARIANT
+		    _IEnumVARIANT-pointer))
+  (begin0
+   (let loop ()
+     (define els (Next i))
+     (if (not els)
+         null
+         (cons (variant-to-scheme els)
+               (loop))))
+   (Release i)))
+
+(define (com-enumerate-to-list obj)
+  (com-enumeration-to-list (com-get-property obj "_NewEnum")))
+
 ;; ----------------------------------------
 ;; Initialize