Ruby：我可以在一个语句中多次使用“或”（||）吗？

Question

Hi I'm trying to make a blackjack game using Ruby and am trying to make the values of the picture cards all = 10. Is it okay to use the code I use below to accomplish this? (this is all happening in my Card class)

def value
  if @number == ("jack" || "queen" || "king")
    10
  else
    @number.to_i
  end
end

Answer 1

You can, but not the way you are using it. You either need to use the entire boolean expression in each portion:

if @number == "jack" || @number == "queen" || @number == "king"

or you can make it simpler by checking the contents of an array:

if ["jack", "queen", "king"].include?(@number)

Answer 2

The parens group things that should be evaluated before other things. So, the above says, evaluate:

 ("jack" || "queen" || "king")

and return the results. Lets try that in irb:

irb(main):004:0> ("jack" || "queen" || "king")
=> "jack"

Since "jack" is truthy there's no need to look at the rest of the list and "jack" is returned.

This will work fine as long as @number is equal to "jack" but not so much for the other values. You want to compare @number against each value until you get a match or exhaust the list. See @PinneyM's answer of

(@number == "jack") || (@number == "queen") ...

Answer 3

That is a valid ruby snippet, but it doesn't do what you think it does: it first evaluates

 ("jack" || "queen" || "king")

which evaluates to "jack" as that is the first non false/nil value. It then compares @card to this, so your code is equivalent to

def value
  if @number == 'jack'
    10
  else
    @number.to_i
  end
end

You could compare each in turn (@number == 'jack') || (@number == 'queen') ||... (@number == 'jack') || (@number == 'queen') ||... , you could use %w(jack queen king).include?(@number) or you could use a case statement:

def value
  case @number
  when 'jack', 'queen', 'king'
    10
  else
    @number.to_i
  end
end