Ruby only checks for first element of a boolean expression?

Question

Here's my code:

array = ["b", "c", "a", "e", "d", "g", "i", "f"]

array.each_index do |letter| 

  if array[letter] == ("a" || "e" || "i" || "o" || "u")

    puts "found #{array[letter]}"

  end

end

I'd expect it to return this:

found a

found e

found i

but instead I only get

found a

What's more, if I change the order of the elements within () on line 3, e.g. like this

if array[letter] == ("e" || "a" || "i" || "o" || "u")

the code returns

found e

instead of

found a

.

I think I understand the problem—Ruby is only checking

array

for the first element within (). But can anyone explain why this is? I'd expect it to check for all of them.

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Answer 1

x || y is x if x is truthy, y otherwise. "a" is truthy (everything except nil and false is truthy, those two and only those two are falsey), therefore "a" || whatever_it_doesnt_matter is always "a".

So,

if array[letter] == ("a" || "e" || "i" || "o" || "u")

is equivalent to

if array[letter] == ("a" || ("e" || ("i" || ("o" || "u"))))

which evaluates to

if array[letter] == ("a" || ("i" || ("o" || "u")))

which evaluates to

if array[letter] == ("a" || ("o" || "u"))

which evaluates to

if array[letter] == ("a" || "u")

which evaluates to

if array[letter] == "a"

Ruby only checks for first element of a boolean expression?

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