Rails 6 adds Enumerable#index_with

Rails 6 added index_with on Enumerable module. This will help in creating a hash from an enumerator with default or fetched values.

Before Rails 6, we can achieve this by calling map along with to_h.

index_with takes both value or a block as a parameter.

Let's checkout how it works.

Rails 5.2

Let's create a hash from an array in Rails 5.2 using map and to_h.

1
2> > address = Address.first
3> > SELECT "addresses".\* FROM "addresses"
4> > ORDER BY "addresses"."id" ASC LIMIT \$1 [["LIMIT", 1]]
5
6=> #<Address id: 1, first_name: "Amit", last_name: "Choudhary", state: "California", created_at: "2019-03-21 10:03:57", updated_at: "2019-03-21 10:03:57">
7
8> > NAME_ATTRIBUTES = [:first_name, :last_name]
9
10=> [:first_name, :last_name]
11
12> > NAME_ATTRIBUTES.map { |attr| [attr, address.public_send(attr)] }.to_h
13
14=> {:first_name=>"Amit", :last_name=>"Choudhary"}
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Rails 6.0.0.beta2

Now let's create the same hash from the array using index_with in Rails 6.

1
2> > address = Address.first
3> > SELECT "addresses".\* FROM "addresses"
4> > ORDER BY "addresses"."id" ASC LIMIT \$1 [["LIMIT", 1]]
5
6=> #<Address id: 1, first_name: "Amit", last_name: "Choudhary", state: "California", created_at: "2019-03-21 10:02:47", updated_at: "2019-03-21 10:02:47">
7
8> > NAME_ATTRIBUTES = [:first_name, :last_name]
9
10=> [:first_name, :last_name]
11
12> > NAME_ATTRIBUTES.index_with { |attr| address.public_send(attr) }
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14=> {:first_name=>"Amit", :last_name=>"Choudhary"}
15
16> > NAME_ATTRIBUTES.index_with('Default')
17
18=> {:first_name=>"Default", :last_name=>"Default"}
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Here is the relevant pull request.