Ruby Case class check

问题

How can I get the following code to work (I want to decide upon an action based on the class of the arg):

def div arg
  material = case arg.class
             when String
               [arg, arg.size]
             when Fixnum
               arg
             end
  material
end

回答1:

The comparison in the case statement is done with the === - also called the case equality operator. For classes like String or Fixnum it defined as to test if the object is an instance of that class. Therefore instead of a class just pass the instance to the comparison by removing the .class method call:

def div arg
  material = case arg
             when String
              [arg, arg.size]
             when Fixnum
              arg
             end
  material
end

In your example, you assign the result of the case block to a local variable material which you return right after the block. This is unnecessary and you can return the result of the block immediately, what makes the method a bit shorter:

def div(arg)
  case arg
  when String
    [arg, arg.size]
  when Fixnum
    arg
  end
end

回答2:

I think I'd prefer:

def div(arg)
  return arg if arg.is_a? Fixnum
  [arg, arg.size] if arg.is_a? String
end

来源：https://stackoverflow.com/questions/43957892/ruby-case-class-check