When the same code is duplicated in two or more separate branches of a conditional, it can make the code harder to understand, maintain, and can
potentially introduce bugs if one instance of the code is changed but others are not.
Having two cases in a switch statement or two branches in an if chain with the same implementation is at
best duplicate code, and at worst a coding error.
if ($a >= 0 && $a < 10) {
doFirst();
doTheThing();
}
else if ($a >= 10 && $a < 20) {
doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
doFirst();
doTheThing(); // Noncompliant; duplicates first condition
}
switch ($i) {
case 1:
doFirst();
doSomething();
break;
case 2:
doSomethingDifferent();
break;
case 3: // Noncompliant; duplicates case 1's implementation
doFirst();
doSomething();
break;
default:
doTheRest();
}
If the same logic is truly needed for both instances, then:
- in an
if chain they should be combined
if (($a >= 0 && $a < 10) || ($a >= 20 && $a < 50)) {
doFirst();
doTheThing();
}
else if ($a >= 10 && $a < 20) {
doTheOtherThing();
}
- for a
switch, one should fall through to the other
switch ($i) {
case 1:
case 3:
doFirst();
doSomething();
break;
case 2:
doSomethingDifferent();
break;
default:
doTheRest();
}
Exceptions
Blocks in an if chain that contain a single line of code are ignored, as are blocks in a switch statement that contain a
single line of code with or without a following break.
if ($a >= 0 && $a < 10) {
doTheThing();
}
else if ($a >= 10 && $a < 20) {
doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
doTheThing(); // no issue, usually this is done on purpose to increase the readability
}
But this exception does not apply to if chains without else-s, or to switch-es without default clauses when
all branches have the same single line of code. In the case of if chains with else-s, or of switch-es with
default clauses, rule S3923 raises a bug.
if ($a >= 0 && $a < 10) {
doTheThing();
}
else if ($a >= 20 && $a < 50) {
doTheThing(); //Noncompliant; this might have been done on purpose but probably not
}
