Rails ActiveSupport Enumerable adds index_with method. This method allows creating hash with a value from block passed or default value. This is useful when we want to create a hash and value needs to be generated with some custom logic.

Background

• Rails Enumerable already has index_by which can be used to index elements of enumerable with a particular key.
• Enumerable#index_with comes in handy when we want a hash with customizable value.

Sample data

Let’s say we have a Post model as given below.

class Post < ApplicationRecord {
                      :id => :integer,
                   :title => :string,
                    :body => :integer
}

We have a post object as given below.

  post = Post.first
  # <Post:0x007fb9b024a218> {
  #                    :id => 162973,
  #                 :title => 'Enumerable index_with',
  #                  :body => 'Use Enumerable#index_with to create hash with customizable value'
  # }

Enumerable#index_with with a block

Now, we can use Enumerable#index_with as given below.

  %i(title body).index_with { |attribute| post.public_send(attribute) }

Output:

  {
    title: 'Enumerable index_with',
    body: 'Use Enumerable#index_with to create hash with customizable value'
  }

Enumerable#index_with with a deafult argument

index_with used whatever passed to it as an argument as a value for each key if block is not used.

Example 1

  %i(title body).index_with(nil)

Output:

  {
    title: nil,
    body: nil
  }

Example 2

  %i(title body).index_with([])

Output:

  {
    title: [],
    body: []
  }

Check out all the available methods on Enumerable to know more about handling Enumerable objects. If you want to try this feature out, compile with Rails master from Github.