array_indices.rb

arr = [9, 5, 1, 2, 3, 4, 0, -1]
# return the element of the Array variable `arr` at the position `index`
def element_at(arr, index)
  arr.at(index) ||
  arr[index]  
end

# return the elements of the Array variable `arr` between the start_pos and end_pos (both inclusive)
def inclusive_range(arr, start_pos, end_pos)
    arr[start_pos..end_pos]
end

# return the elements of the Array variable `arr`, start_pos inclusive and end_pos exclusive
def non_inclusive_range(arr, start_pos, end_pos)
    arr[start_pos...end_pos]
end

# return `length` elements of the Array variable `arr` starting from `start_pos`
def start_and_length(arr, start_pos, length)
  arr[start_pos,length]
end