`-': nil 不能被强制转换为 Fixnum (TypeError)

Question

在我的程序中，我收到一个错误，上面写着 ./ruby_camping.rb:91:in `-': nil can't be coerced into Fixnum (TypeError)。我想做的是结帐我刚刚签到的客人。这是结帐部分的代码块：

def self.check_out 
  puts "Welcome to checkout!"
  puts $camping.current_guests
  puts " Here are the current guests, who do you want to checkout?!" 
  puts "State plot number "
  plot = gets.chomp.to_i
  guest = $camping.current_guests[plot-1] 
  puts "State the date for your checkout (a number bigger then " + guest.arrived.to_s + "): "
  # it should not be possible for a guest to checkout before she has checked in
  departureDate = gets.chomp.to_i
  guestStayedDays = departureDate - guest.arrived #Days the guest has stayed
  while (guestStayedDays < 1) do                        
   puts "The date for checkout is not valid. The guest checked in " + guest.arrived.to_s
   puts "Please state a new date."
   departureDate = gets.chomp.to_i
   guestStayedDays = departureDate - guest.arrived
  end       
  guest.departure = departureDate
  guest.plot.increase(guestStayedDays) # increases the electricity meter
  puts guest # prints the guest
  $camping.current_guests[plot-1] = nil # emptys the plot
 end
end

departmentDate怎么还是nil呢？感谢您的帮助！

Answer 1

要获得更详细的答案，您必须在程序中指出哪一行是第 91 行。但是，要指出正确的方向，如果您看到的是nil can't be coerced into Fixnum，那么这意味着- 的右侧 是nil。例如

irb(main):001:0> 5 - nil
TypeError: nil can't be coerced into Fixnum
        from (irb):1:in `-'
        from (irb):1

从你的代码中我能看到的唯一可能的例子是guestStayedDays = departureDate - guest.arrived，所以我会检查guest.arrived的值。

如果- 的左侧 是nil，例如departureDate 或 plot 那么你会得到 undefined method '-' for nil:NilClass 。