如何在 Ruby (v2.6.3) 中获取随机数

Question

I'm doing an assignment in which I have to make a simple card game. The tutor has provided me with a method to generate a random card - which I'm not allowed to change:

def random_card
  cards = ["two", "three", "four", "five", "six", "seven",
           "eight", "nine", "ten",
           "jack", "queen", "king", "ace"]

  cards[rand(13)]
end

And I have tried to make a method that adds cards to the players hand, calling the random_card method each time:

def move(random_card)
  player_hand = []
  while true do
    puts "Make a move. Enter 'hit' or 'stick' "
    choice = gets.chomp
    if choice == "stick"
      break
    elsif choice == "hit"
      # this is currently giving me the same card for each "hit"
      # but a different one each time I run the code.
      player_hand.push(random_card)
    end
  end
  # TODO change this to return
  puts player_hand
end

Each time I `hit' the same card gets added to the hand, My question is how to prevent this and for the method to return a "new" random card each time we run through the loop.

Thanks.

Answer 1

You've used the name random_card for two different things: 1) the method given you by your instructor; and 2) the name of the argument to your move method.

The second usage defines a local variable, which masks (or shadows) the method name. In other words, within the move method random_card refers to whatever value you passed in when you called move . It does not call the method.

Here's a simple illustration:

def foo
  %w(hi hey howdy)[rand 3]
end

def bar1
  puts foo
end

def bar2(foo)
  puts foo
end

5.times { bar1 }  # produces a random selection of hi's, hey's, and howdy's
puts
5.times { bar2 "Help!  I'm stuck!" }  # prints the passed message 5 times
puts
5.times { srand 12345; bar1 }  # produces "howdy" 5 times

Given what you've shown, you probably don't need an argument to move . If you do, give it its own name. Also make sure you aren't messing with srand somewhere else in your program.

---

Yet another alternative would be to indicate that you want to use the method rather than the argument with the same name by using parentheses. With the example above, change bar2 to:

def bar2(foo)
  puts foo()
end

The empty parentheses make it clear this is an invocation of the method foo , not a reference to the (now unused) argument foo .

Answer 2

here is the simple solution to your problem

def random_card
  cards = ["two", "three", "four", "five", "six", "seven",
           "eight", "nine", "ten",
           "jack", "queen", "king", "ace"]

  cards[rand(13)]
end

def move(callback)
  player_hand = []
  while true do
    puts "Make a move. Enter 'hit' or 'stick' "
    choice = gets.chomp
    if choice == "stick"
      break
    elsif choice == "hit"
      player_hand.push(callback.call)
    end
  end
  puts player_hand
end

and you can call this method as

move(method(:random_card))