A case and a chain of if/elsif statements is evaluated from top to bottom. At most, only one branch will be
executed: the first one with a condition that evaluates to true.
Therefore, duplicating a condition automatically leads to dead code. Usually, this is due to a copy/paste error. At best, it’s simply dead code and
at worst, it’s a bug that is likely to induce further bugs as the code is maintained, and obviously it could lead to unexpected behavior.
For a case, the second when will never be executed, rendering it dead code. Worse there is the risk in this situation
that future maintenance will be done on the dead case, rather than on the one that’s actually used.
Noncompliant code example
if param == 1
openWindow()
elsif param == 2
closeWindow()
elsif param == 1 # Noncompliant
moveWindowToTheBackground()
end
case i
when 1
# ...
when 3
# ...
when 1 # Noncompliant
# ...
else
# ...
end
Compliant solution
if param == 1
openWindow()
elsif param == 2
closeWindow()
elsif param == 3
moveWindowToTheBackground()
end
case i
when 1
# ...
when 3
# ...
else
# ...
end
