Making use of a fall-through switch

Question

While researching for better ways to make use of a switch statement, I found this stackoverflow example. I wanted to do something similar, but with a twist:

switch($status)
{
 case "a":
 case "b":
  echo "start execute code for case a and b";
 case "a":
  echo "continue to execute code for case a only";
 case "b":
  echo "continue to execute code for case b only";
 case "a":
 case "b":
  echo "complete code execution for case a and b";
 break;
 case "c":
  echo "execute code for case c";
 break;
 case "d":
  echo "execute code for case d";
 break;
 case "e":
  echo "execute code for case e";
 break;
 case "f":
  echo "execute code for case f";
 break;
 default:
  echo "execute code for default case";
}

Yes, the above obviously doesn't work out as planned because case "a" will fall-through through until it hits a break. I just want to know whether there is a way to do this elegantly without repeating too much code.

This is usually called fall-through; I don't think I've seen it called "cascade" until now. — NullUserException, Apr 06 '12 at 15:25
Getting "clever" is a bad idea. The kind of thing you are trying to do will make your code harder to understand and is very likely to lead to very hard-to-find bugs down the road. Keep it simple. — Carl Manaster, Apr 06 '12 at 15:45

score 12 · Answer 1 · answered Apr 06 '12 at 16:02

Here is what I think would be an elegant solution:

switch($status)
{
 case "a":
 case "b":
  echo "start execute code for case a and b";
  if($status == "a") echo "continue to execute code for case a only";
  if($status == "b") echo "continue to execute code for case b only";
  echo "complete code execution for case a and b";
 break;
 case "c":
  echo "execute code for case c";
 break;
 case "d":
  echo "execute code for case d";
 break;
 case "e":
  echo "execute code for case e";
 break;
 case "f":
  echo "execute code for case f";
 break;
 default:
  echo "execute code for default case";
}

I am not trying to invent anything new here. Just trying to learn from the experiences of everyone here. Thanks to all who provided me with answers.

Don't know why this isn't ranked higher. This is the simplest solution and also the most legible for future maintainers of the code. — Jazz, Apr 06 '12 at 16:27

score 6 · Answer 2 · answered Apr 06 '12 at 15:26

6

Once a case is matched, PHP will ignore any further case statements and execute ALL code until either the switch is closed (}) or a break is encountered. break will also terminate the switch, so what you want is not possible.

answered Apr 06 '12 at 15:26

Marc B

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1

It is certainly *possible*; the OP just has to use if/elseif/else. – NullUserException Apr 06 '12 at 15:27
@NullUserException: which'd just make things even more illegible. Might as well just stick with if/then/else to begin with. – Marc B Apr 06 '12 at 15:28
1

That's what I meant: just use if/elseif/then, no switch statements. – NullUserException Apr 06 '12 at 15:30

Colin D · Answer 3 · 2012-04-06T15:37:40.800

This is not correct switch statement usage.

You should replace your switch with a series of if statements.

if($status == a || $status == b ) {
   echo "start execute code for case a and b";
   if(status == a) {
      echo "continue to execute code for case a only";
   }
   else {
      echo "continue to execute code for case b only";   
   }
   echo "complete code execution for case a and b";
}
else if ($status == c) {
   echo "execute code for case c";  
}
...
...
else {
   echo "execute code for default case";
}

score 1 · Answer 4 · answered Apr 06 '12 at 15:50

There is no how in the would $status can be = a AND b except if its a array i kno what you want to do and this is my prove of concept

function runSwitch($status) {

    if (in_array ( "a", $status ) && in_array ( "b", $status )) {
        echo "start execute code for case a and b" . PHP_EOL;
    }

    if (in_array ( "a", $status )) {
        echo "continue to execute code for case a only" . PHP_EOL;
    }

    if (in_array ( "b", $status )) {
        echo "continue to execute code for case b only" . PHP_EOL;
    }

    if (in_array ( "c", $status )) {
        echo "execute code for case c" . PHP_EOL;
    }

    if (in_array ( "d", $status )) {
        echo "execute code for case d" . PHP_EOL;
    }

    if (in_array ( "e", $status )) {
        echo "execute code for case e" . PHP_EOL;
    }

    if (in_array ( "f", $status )) {
        echo "execute code for case f" . PHP_EOL;
    }

    if (in_array ( "c", $status ) && in_array ( "f", $status )) {
        echo "continue to execute code for case c AND f only" . PHP_EOL;
    }

}

Example 1

$status = array (
        "a" 
);

runSwitch($status);

Output

continue to execute code for case a only

Example 2

$status = array (
        "a" , "b"
);


runSwitch($status);

Output

start execute code for case a and b
continue to execute code for case a only
continue to execute code for case b only

I hope this helps

Thanks

thanks for your help, but $status is a single character string, not an array. I think I know how to do it. I am just amuse at the kind of response I am getting by others. — Question Overflow, Apr 06 '12 at 15:57

score 0 · Answer 5 · answered Apr 06 '12 at 15:38

0

As Marc B said what you're trying (at least with a switch) can't be done. Fortunately a good way to remove duplicate code is to define methods, that way code common to both a and b can be called when required.

answered Apr 06 '12 at 15:38

Jim

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Making use of a fall-through switch

5 Answers5