如何将 (2-∞) 参数传递给 ruby​​ 方法？

Question

I'm working on a very simple exercise: a method that can multiply between two and an indefinite number of floats. My first idea for doing this was to use the splat operator:

def multiply a, b, *rest
  a * b * rest
end

That was unsuccessful. I then tried this:

def multiply *numbers
  total = 1
  numbers.each do |x|
   total = total * x 
  end
  total
end

The above is almost successful—the problem is that it will accept a single argument, and I want it to require at least two. How can I achieve this?

Answer 1

There are many options. The one the author of the exercise probably intended for you to use is inject :

def multiply(*numbers)
  numbers.inject(&:*)
end

This will cause the same problem as your second implementation of multiply in that it will accept 0 or 1 arguments. You can fix this by simply raising an ArgumentError if you don't have at least two:

def multiply(*numbers)
  raise ArgumentError unless numbers.length >= 2
  numbers.inject(&:*)
end

You can go the other way and accept two actual arguments and splat the rest, and simply build the complete array you intend to multiply together:

def multiply(a, b, *rest)
  [a, b, *rest].inject(&:*)
end