Why is this an issue?

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
}

value match {
  case 1 =>
    doFirstThing
    doSomething
  case 2 =>
    doSomethingDifferent
  case 3 => // Noncompliant; duplicates case 1's implementation
    doFirstThing
    doSomething
  case _ =>
    doTheRest
}

If the same logic is needed for both instances, then:

• in an if structure they should be combined

if ((a >= 0 && a < 10) || (a >= 20 && a < 50)) {
  doFirstThing
  doTheThing
}
else if (a >= 10 && a < 20) {
  doTheOtherThing
}
else {
  doTheRest
}

• for a match, the values should be put in the case expression list.

value match {
  case 1 | 3 =>
    doFirstThing
    doSomething
  case 2 =>
    doSomethingDifferent
  case _ =>
    doTheRest
}

Exceptions

Blocks in an if chain that contain a single line of code are ignored, as are blocks in a match statement that contain a single line of code.

if(a == 1) {
  doSomething  //no issue, usually this is done on purpose to increase the readability
} else if (a == 2) {
  doSomethingElse
} else {
  doSomething
}

But this exception does not apply to if chains without else-s, or to match-es without default clauses when all branches have the same single line of code. In case of if chains with else-s, or of match-es with default clauses, rule {rule:scala:S3923} raises a bug.

if(a == 1) {
  doSomething  //Noncompliant, this might have been done on purpose but probably not
} else if (a == 2) {
  doSomething
}

Resources

Related rules

• {rule:scala:S3923} - All branches in a conditional structure should not have exactly the same implementation