Re: return type for a method parameter & assigning probe buttons

[Marcus G. Daniels]

>>>>> "WS" == William S Shu <address@hidden> writes:

WS> Problem 1: Objective-C) How can one pass a method as an argument
WS> as well as the type of its return value? 

In Swarm, the way selectors are called is via the `perform' method.
Since this method is typed to return an object, selectors should all be for
methods that return objects.

Generic return typing is hairy problem.  If you really want to be
able to return generic types you need to use GCC builtins and the
performv: method.  Something like this:

- (double)call: (SEL)sel
{
  __builtin_return ([self performv: sel : __builtin_apply_args ()]);
}

Unfortunately the __builtin_{return/apply_args} are deprecated in GCC
and actually fail on some platforms (e.g. Sparc).  (For Java things,
we take care of argument frame packing and unpacking by hand, using platform
specific code.)

WS> // valueOf takes *no* argument
WS> - (Real)getValueBL: (Point)bL TR: (Point)tR
WS>       class: (id)aClass  order: (int)type value: (SEL)valueOf {
WS>  id obj;
WS>  int i, j;
WS>  Real val;
WS> ...
WS>      obj = [self getWorldObjectAtX: i Y: j];
WS>      if ([obj isKindOf: aClass]) {
WS>        ....
WS>        val += [obj valueOf]    <====== **** return type assumed to be id

This is actually invalid syntax.  You'd have to say [obj perform: valueOf].

WS>     How do I get to probe both objects (in fact any object) on the
WS> raster by using the same mouse button.

WS>  [worldRaster setButton: ButtonRight   // use Right button
WS>               Client: personDisplay
WS>               Message: M(makeProbeAtX:Y:)];

Send a different message, one that has the effect of calling
makeProbeAtX:Y: twice.


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