Gotcha with Ruby's Else Statement

April 5, 2011

I came across a strange gotcha with the else statement in ruby.

As it turns out, you can place an expression directly after an else statement:

if false
  puts "you'll never see this"
else false
  puts "you'll always see this"

At first I chalked it down as a flaw in the grammar, but it makes sense when you examine it. The ruby grammar expects an expression to follow else. It does not necessarily have to occur on the next line. A line break separates the false and the puts statement following the else. In this case, if the else statement is to be entered at all, the expression on the same line will always be evaluated, as will the code segment that follows within the else clause.

This may seem silly but I caught a fairly serious bug that came as the result of someone using an else instead of an elsif. Sometimes it’s fun to dissect an interesting edge case in the language.