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) // Noncompliant; duplicates first condition
{
DoFirst();
DoTheThing();
}
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
The rule does not raise an issue for blocks in an if chain that contain a single line of code. The same applies to 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) //no issue, usually this is done on purpose to increase the readability
{
DoTheThing();
}
However, this exception does not apply to if chains without an else statement or to a switch statement
without a default clause when all branches have the same single line of code.
if (a == 1)
{
DoSomething(); // Noncompliant, this might have been done on purpose but probably not
}
else if (a == 2)
{
DoSomething();
}
