Ruby Grocery List Program Question

Question

I built out the grocery list program in the Ruby Collections section and I don't understand how Ruby knows that I want to assign 'item_name' and 'quantity' variables to the key/value pair in the array created in the hash, which is associated with the "items" hash key.

In the 'add_list_item' method created, I reference the hash created in the 'create_list' method but I don't explicitly assign the 'item_name' and 'quantity' variables/hash values to the "items" hash key. The code in the 'add_list_item' reads, "hash = {"name" => item_name, "quantity" => quantity}". How does ruby know that the hash value I am referring to is associated with the "item" hash key created in the 'create_list' method?

Does Ruby implicitly associate the 'item_name' and 'quantity' variable values to the hash key "items", based on the fact that it is the only empty hash value in the 'hash' hash?

I hope the above makes sense. I am new to Ruby and programming in general. Any info here would be much appreciated. Below is the program code in question.

def create_list
  print "What is the name of your list? "
  name = gets.chomp

  hash = { "name" => name, "items" => Array.new}
end


def add_list_item
  print "What is the item called? "
  item_name = gets.chomp

  print "How much? "
  quantity = gets.chomp.to_i

  hash = {"name" => item_name, "quantity" => quantity}
  return hash
end


def print_separator(character = "-")
  puts character * 80
end


def number_of_items
  puts "How many items would you like to add? "
  num_items = gets.chomp.to_i
  return num_items
end


def print_list (list)
  puts "list: #{list["name"]}"
  print_separator()
  list["items"].each do |item|
      puts "\tItem: " + item["name"] + "\t\t\t" + "Quantity: " + item["quantity"].to_s
  end
    print_separator()
end


list = create_list()
num = number_of_items()
num.times {list["items"].push(add_list_item())}
print_list(list)
p list

Answer 1 · 2017-07-09T22:38:39Z

July 9, 2017 10:38pm

Does Ruby implicitly associate the 'item_name' and 'quantity' variable values to the hash key "items", based on the fact that it is the only empty hash value in the 'hash' hash?

Ruby doesn't implicitly assign the returned hash from the add_list_item method to the "items" key in your list hash. Instead you're telling Ruby to push a new hash value into the "items" array value. Take a look at these sections of your program:

def create_list
  print "What is the name of your list? "
  name = gets.chomp

  hash = { "name" => name, "items" => Array.new}
end

...

list = create_list()
num = number_of_items()
num.times {list["items"].push(add_list_item())}

In the first snippet is your create_list method which returns a new hash with a "name" key assigned to the name provided by user input. The other key in this hash, "items", is initialized as an empty array value.

The second snippet shows where you create a new variable named list which initializes using the create_list method as a list hash. You're adding new list items by calling list["items"].push(add_list_item()) which uses the Array.push method to append a new hash value returned from the add_list_item method into the list["items"] array.

I hope that helps clear up what Ruby is doing here. Because the data type of the "items" key in the list hash is an array you can simply use array methods like push to append new array values. In this case the data value being pushed to the items array is a new hash with keys for the item name and quantity.

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seantipton

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Ruby Grocery List Program Question

1 Answer

Joe Purdy

Joe Purdy