Ruby: Remove first and last element of an Array - why the solution works one way & not the other

Question

I's like to know why the second solution works but the first one, which has chained methods, doesn't work.

This chained method doesn't work:

nopers = [5, 6, 7, 8, 9]

class Array
  define_method(:trimy) do
    self.shift().pop()
  end
end

When I test it, nopers.trimy(), it gives an undefined error message. "method 'pop' for 1:Fixnum, in 'block in '" and only executes the .pop() method, removing the 5.

But, this version works:

yuppers = [1, 2, 3, 4, 5, 6]

class Array
  define_method(:trim) do
    self.shift()
    self.pop()
  end
end

yuppers.trim()

When I test it, yuppers gives me: [2, 3, 4, 5]

Answer 1

I would say that:

yuppers[1..-2]

is the most simple solution

Answer 2

This is because both shift and pop return the value that is removed:

[1, 2, 3].pop   # => returns 3
[1, 2, 3].shift # => returns 1

So when you chain them together you're calling #pop on the result of #shift, which is an Integer which isn't allowed.