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Ruby

How do I return a boolean when an array is empty?

This is the question I'm currently working with:

In the TodoList class, fill in the empty? method to return a boolean value. The empty? method should return true if there are no elements in the @todo_items array. The method should return false if there is more than one element in the @todo_items array.

Here is the code as it was:

class TodoList
  attr_reader :name, :todo_items

  def initialize(name)
    @name = name
    @todo_items = []
  end

  def add_item(name)
    todo_items.push(TodoItem.new(name))
  end

  def empty?
    if @todo_items = nil
        return true
      else
        return false
  end
end

and one of my solutions:

  def empty?
    if @todo_items = nil
        return true
      else
        return false
  end

I've tried "[]" "[""]" "0"

I've also tried: @todo_items.nil? @todo_items.any?

9 Answers

William Li
PLUS
William Li
Courses Plus Student 26,867 Points

First, you can NOT check if an Array is empty by checking it against nil

[] == nil   # => false

This doesn't work, empty Array doesn't equal to nil

Now for you problem, you can make use of the Array build-in method empty? to do the job http://ruby-doc.org//core-2.2.0/Array.html#method-i-empty-3F

def empty?
  todo_items.empty?
end

alternatively, you can tell if Array is empty by checking its length

def empty?
  todo_items.length == 0
end
William McManus
William McManus
14,819 Points

That first bit was brilliant! Guess there was a hint in the Array name huh:)

Hunter Garrett
Hunter Garrett
6,339 Points

I wrote

def empty?
    if todo_items.length == 0
      return true
    elsif todo_items.length > 1
      return false
    end

I think your problem is that you're assigning instead of comparing with your conditional statements. "=" vs. "==" look at your if statements

Thank you both for your answers. I actually was missing an "end". :|

William, thank you for the additional information about nil.

You don't need to use the @ for the instance variable since todo_items is already defined in the attr_reader method.

Kasia Ekiert
PLUS
Kasia Ekiert
Courses Plus Student 13,248 Points

def empty? if @todo_items != [] empty = false else empty ||= true end end

Carlos Carrillo
Carlos Carrillo
15,596 Points

I did it like this:

if @todo_items == [] return false else return true end

def empty?
    answer = false
    if todo_items.length == 0
      answer = true
    end
    return answer
 end
class TodoList
  attr_reader :name, :todo_items

  def initialize(name)
    @name = name
    @todo_items = []
  end

  def add_item(name)
    todo_items.push(TodoItem.new(name))
  end

  def empty?
    @todo_items == [] ? true : false
  end

end