A switch and a chain of if/else if statements is evaluated from top to bottom. At most, only one branch will
be executed: the first one with a condition that evaluates to true.
Therefore, duplicating a condition automatically leads to dead code. Usually, this is due to a copy/paste error. At best, it’s simply dead code and
at worst, it’s a bug that is likely to induce further bugs as the code is maintained, and obviously it could lead to unexpected behavior.
For a switch, if the first case ends with a break, the second case will never be executed, rendering it dead code. Worse
there is the risk in this situation that future maintenance will be done on the dead case, rather than on the one that’s actually used.
On the other hand, if the first case does not end with a break, both cases will be executed, but future maintainers may not notice
that.
Noncompliant code example
if ($param == 1)
openWindow();
else if ($param == 2)
closeWindow();
else if ($param == 1) // Noncompliant
moveWindowToTheBackground();
switch($i) {
case 1:
//...
break;
case 3:
//...
break;
case 1: // Noncompliant
//...
break;
default:
// ...
break;
}
Compliant solution
if ($param == 1)
openWindow();
else if ($param == 2)
closeWindow();
else if ($param == 3)
moveWindowToTheBackground();
switch($i) {
case 1:
//...
break;
case 3:
//...
break;
default:
// ...
break;
}
