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) {
doFirstThing();
doTheThing();
}
else if (a >= 10 && a < 20) {
doTheOtherThing();
}
else if (a >= 20 && a < 50) {
doFirstThing();
doTheThing(); // Noncompliant; duplicates first condition
}
else {
doTheRest();
}
switch (i) {
case 1:
doFirstThing();
doSomething();
break;
case 2:
doSomethingDifferent();
break;
case 3: // Noncompliant; duplicates case 1's implementation
doFirstThing();
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)) { // Compliant
doFirstThing();
doTheThing();
}
else if (a >= 10 && a < 20) {
doTheOtherThing();
}
else {
doTheRest();
}
- for a
switch, one should fall through to the other
switch (i) {
case 1:
case 3: // Compliant
doFirstThing();
doSomething();
break;
case 2:
doSomethingDifferent();
break;
default:
doTheRest();
}
When all blocks are identical, either this rule will trigger if there is no default clause or rule S3923 will raise if there is a
default clause.
Exceptions
Unless all blocks are identical, blocks in an if chain that contain a single line of code are ignored. The same applies to blocks in a
switch statement that contains a single line of code with or without a following break.
if (a == 1) {
doSomething(); // Compliant, usually this is done on purpose to increase the readability
} else if (a == 2) {
doSomethingElse();
} else {
doSomething();
}
