[cable] passing number &'s to method

[Steve Pieper]

Brad -

Amazing - works like a charm!

Don't apologize about this, it's all very logical.  I had been thinking 
something like this might have already been built in, but no matter. 
Your one little class can handle all these situations nicely (at least 
the ones I need at the moment).

The example call findAndGetSint16 was in fact a class method, so I 
didn't run into any of the namespace level function issues you mentioned.

Thanks for your help and for providing such a great tool!

-Steve



Brad King wrote:
> Steve,
> 
> 
>>I'm trying my first Cable project and I hope this is an easy question for
>>you: in Tcl, how can I pass the second argument to the following method?
>>
>>	OFCondition findAndGetSint16(const DcmTagKey&, short&)
>>
>>The OFCondition and DcmTagKey classes are wrapped up and working nicely,
>>and I can call a similar method to get a string type... but I don't know
>>what to do about the basic types (I also need int, float, double, etc but
>>I assume they'll all fit the same pattern).
>>
>>Background: I'm trying to wrap the DCMTK tools from University of
>>Oldenberg - a very nice dicom implementation you can find at
>>http://dicom.offis.de.  I plan to try hooking up their code into vtk/itk
>>at the tcl level.  So far CMake and Cable have worked great (until I hit
>>this question).
>>
> 
> Since the second argument is a reference type, a Tcl variable cannot be
> passed directly to it.  The reason is that after the call is made, there
> is no way for the wrappers to know where to place the value for Tcl to
> find.  You will need to implement a wrapper in C++ to provide the value to
> you without a reference.  If you have a C++ method return a short& type,
> then it will pass the second argument without a problem.
> 
> For example:
> 
> template <typename T>
> class ReferencePasser
> {
>   T n;
> public:
>   ReferencePasser(): n(0) {}
>   ReferencePasser(T i): n(i) {}
>   T& Pass() { return n; }
>   T Get() const { return n; }
>   void Set(T i) { n = i; }
> };
> 
> Wrapping "ReferencePasser<short>" as ReferencePasser_short will allow the
> following in Tcl:
> 
> # Wrap the findAndGetSint16 method of foo.
> proc FindAndGetSint16 { foo key result } {
>   upvar $result res
>   set srp [ReferencePasser_short 0]
>   set val [$foo findAndGetSint16 $key [$srp Pass]]
>   set res [$srp Get]
>   return $val
> }
> 
> This assumes that "foo" is an instance of a class with a findAndGetSint16
> method.  If findAndGetSint16 is a namespace-level function, I would
> suggest writing a class that wraps all such functions and hides these
> details.  Cable doesn't deal with namespace-level functions very well
> right now, and an upcoming re-write (currently in a cvs branch) will not
> support them at all for a while.  Both versions deal with static methods
> in a class with no trouble, though.
> 
> I know that the above is very, very ugly, and I wish I had a better
> solution right now.  This problem is on my wish-list of things to fix in
> the future.
> 
> -Brad
> 
>