each_with_object method

The each_with_object method takes an enumerable collection and iterates through all its elements, building an object as it goes. It returns the object.

This method is shorthand for a common programming idiom:

def get_sum list
  sum = 0

  list.each{|item| sum += item}

  return sum
end

Instead, we can use each_with_object to achieve this in one line:

list.each_with_object(0){|item, sum| sum += item} 

For simple examples like this, the inject/reduce methods actually work better, but each_with_object's value is in building more complex objects.

Pet Inventory

# list of pet names:
inventory.each_with_object([]){|pet, array| array << pet.name}
    #=> ["dog", "cat", "fish", "scorpion", "beetle", "monkey", "rock"]

# hash of pet names/quantities:
inventory.each_with_object({}){|pet, hash| hash[pet.name] = pet.quantity}
    #=> {"dog"=>100, "cat"=>50, "fish"=>1000, "scorpion"=>1, "beetle"=>10000, "monkey"=>2, "rock"=>0}

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