Workaround for the Scoping Gotcha

My colleague pointed out to me today that you can get around the scoping issue I mentioned by writing your method like this :

 
  Method f() {
    set x = 6
    set m = "write !,"_x ; difference
    xecute m
  }
 

What's the difference? Instead of including the name of the variable x inside the string, you concatenate the value of the local variable x with the string at run-time, before the string is finally evaluated. Because the value of x is resolved before the xecute, things work as you'd expect.

That's true. But I still regard this as a serious bug. An equivalent python program :

 
class A :
    def f(self) :
        x = 6
        m = "print x"
        exec m

x = 9
a = A()
a.f()
 

prints what you'd expect : the number 6.

What's really going on to cause this issue in Caché? My guess is that the OO layer in Caché is compiled down to plain Caché .int routines which don't have a significantly different semantics or scoping rules to Caché ObjectScript. In order to get the effect of the private world inside the object, at compile time the variable x is renamed to some object-specific equivalent. Of course, this renaming affects the real references to x, but not the string assigned to m.

When the VM then tries to xecute the string, it encounters the name x but finds no binding in the local execution frame and so, according to COS's dynamic scoping rules, has to look down the stack for a frame which does have a binding, the place from which we call y.f(), where x is bound to 9.

Of course, this hypothesis might be completely wrong. Expert correction is welcome.