Check if exactly one of a set of conditions is met

Richard_Russell

Raymond Chen seems to think that this technique of testing whether exactly one of a set of conditions is met is a neat idea, so who am I to disagree? Here's a conversion to BBC BASIC:

      Widgets = 0
      Gadgets = 1
      Doodads = 4
      Sockets = 4

      IF FNDoesExactlyOneConditionApply THEN
        PRINT "Exactly one condition applies"
      ELSE
        PRINT "Fewer or more than one condition applies"
      ENDIF
      END

      DEF FNDoesExactlyOneConditionApply
      LOCAL t() : DIM t(2)
      t() = (Widgets = 1), (Gadgets = 1), (Doodads > Sockets)
      = (SUM(t()) = TRUE)

Why (and if) it's better than just adding the conditions together, as one of the commenters suggests, I'm not sure:

      DEF FNDoesExactlyOneConditionApply
      = (Widgets = 1) + (Gadgets = 1) + (Doodads > Sockets) = TRUE

Something about this not being allowed in a 'type-safe' language? I suppose storing Booleans in an array may be more 'legitimate' than adding them together (they're not strictly numbers after all) but I'm out of my depth here.