CODEWITHSUNDEEP
ruby-on-railsrubyruby-on-rails-3
Bohn
Bohn

Reputation: 26919

When do we know we should use a symbol?

Here is a code I am trying to understand and the confusing part for now is the :product_id in the code, specially the ":" part of ":product_id" My question is how should we know we should use that ":" ? 

def up
    # replace multiple items for a single product in a cart with a single item
    Cart.all.each do |cart|
      # count the number of each product in the cart
      sums = cart.line_items.group(:product_id).sum(:quantity)

      sums.each do |product_id, quantity|
        if quantity > 1
          # remove individual items
          cart.line_items.where(product_id: product_id).delete_all

          # replace with a single item
          item = cart.line_items.build(product_id: product_id)
          item.quantity = quantity
          item.save!
        end
      end
    end
  end

Upvotes: 1

Views: 97

Answers (2)

joscas
joscas

Reputation: 7674

Symbols are just pointers to an object containing its name while strings are always different objects.

If you are going to repeat a name many times in your code then use one symbol which is the equivalent of using just one object.

For example if you use the string "France" a 100 times in your code, you would prefer to use :France. The advantage is that in the first case you would instantiate a 100 objects and in the second case just one.

In your example, maybe you are getting confused because product_id: product_id is a Hash represented in JSON style. This would be the equivalent of :product_id => product_id

Upvotes: 2

Akash
Akash

Reputation: 5221

Symbols:

  • are basically string constants
  • are created once. i.e. :product_id will be the same object whenever you use it. Hence they save memory. On the other hand if you write "product_id" multiple times, you are basically creating as many string objects
  • cannot take the benefit of Reg-ex and interpolation(mostly) unless you use a to_s method on a symbol

In a nutshell, use symbols for short string constants which you don't need to process or modify.

Eg: Symbols are great for keys in Hashes etc. Get it?

Upvotes: 3

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