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Ruby

Posted by James Casavant
James Casavant
21,522 Points

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 26,868 Points
William Li
William Li
Courses Plus Student 26,868 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
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
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
David Tonge
PLUS
David Tonge
Courses Plus Student 45,640 Points
David Tonge
David Tonge
Courses Plus Student 45,640 Points

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

James Casavant
James Casavant
21,522 Points
James Casavant
James Casavant
21,522 Points

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

William, thank you for the additional information about nil.

Darrell Padua
Darrell Padua
7,895 Points
Darrell Padua
Darrell Padua
7,895 Points

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
Kasia Ekiert
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
Carlos Carrillo
Carlos Carrillo
15,596 Points

I did it like this:

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

eddyak
eddyak
5,830 Points
eddyak
eddyak
5,830 Points 
def empty?
    answer = false
    if todo_items.length == 0
      answer = true
    end
    return answer
 end
Aaron Cleveland
Aaron Cleveland
1,971 Points
Aaron Cleveland
Aaron Cleveland
1,971 Points 
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