Re: ensuring unreachability

Leif Roar Moldskred <leifm@huldreskog.localdomain>
Tue, 17 Feb 2015 13:54:16 -0600
Andreas Leitgeb <> wrote:

Recently I came across a snippet like this:
 switch (someEnumVar) {
   case E1:
     if (...) {
       ...; return;
     } else if (...) {
       ...; throw ...;
     } else {
       ...; continue; // enclosing loop
   case E2: ...

No fall-through is supposed to ever happen from case E1 to case E2.
All branches in "case E1" exit abnormally. But due to the complexity
it isn't overly obvious.

I'd read that as an indication that you're working at the wrong level
of abstraction.

If it's too much work / too brittle to rewrite the whole thing to a
more manageable form, you could try something like this:

while( ... ) {
 CaseDecision decision;

 switch (someEnumVar) {
  case E1: decision = decideForE1( ... ); break;
  case E2: decision = decideForE2( ... ); break;
  default: throw new RuntimeException( "Program logic error: Not all enums accounted for in switch");
 } // end switch

 switch (decision) {
  case RETURN: return;
  case BREAK: break;
  case CONTINUE: continue;
  default: throw new RuntimeException( "Program logic error: Not all enums accounted for in switch");
} // end loop

Leif Roar Moldskred

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