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() // Noncompliant; duplicates first condition
doTheThing()
} else {
doTheRest()
}
switch i {
case 1:
doFirstThing()
doSomething()
case 2:
doSomethingDifferent()
case 3: // Noncompliant; duplicates case 1's implementation
doFirstThing()
doSomething()
default:
doTheRest()
}
If the same logic is needed for both instances, then:
- in an
if statement, they should be merged.
if (a >= 0 && a < 10) || (if a >= 20 && a < 50) {
doFirstThing()
doTheThing()
} else if a >= 10 && a < 20 {
doTheOtherThing()
} else {
doTheRest()
}
- for a
switch, the values should be put in the case expression list.
switch i {
case 1, 3:
doFirstThing()
doSomething()
case 2:
doSomethingDifferent()
default:
doTheRest()
}
Exceptions
case labels that declare variables cannot have multiple patterns. Therefore this situation is ignored.
switch a {
case .STR_CASE(let x):
print(x)
case .INT_CASE(let x):
print(x)
default:
print("default")
}
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 { // no issue, usually this is done on purpose to increase the readability
doTheThing()
} else if a >= 10 && a < 20 {
doTheThing()
} else if a >= 20 && a < 50 {
doFirstThing()
}
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 { // Noncompliant, this might have been done on purpose but probably not
doTheThing()
} else if a >= 10 && a < 20 {
doTheThing()
}
