Ruby Data Class: Syntax

This content originally appeared on DEV Community and was authored by Kelly Popko

What is Ruby's Data class?

The Data class was introduced to Ruby in Ruby 3.2, to:

'define simple classes for value-alike'
store immutable atomic values

Create the blueprint (instance of Data class)

We call Data.define and pass keyword arguments.

Book = Data.define(:title, :author, :year)

We can define methods as well if we pass it a block.

Book = Data.define(:title, :author, :year) do
  SUMMARY = '%<title>s was written by %<author>s in %<year>i.'

  def to_s
    SUMMARY % {title:, author:, year:}
  end
end

hobbit = Book.new("The Hobbit", "J.R.R. Tolkien", 1937)
puts hobbit
# => nil
'The Hobbit was written by J.R.R. Tolkien in 1937.'

Building from the blueprint

Call .new or use [] notation
Use keyword or positional arguments

`.new` + keyword arguments

hobbit = Book.new(title: "The Hobbit", author: "J. R. R. Tolkien", year: 1937)
# => <data Book title="The Hobbit", author="J. R. R. Tolkien", year=1937>

hobbit.author
# => "J. R. R. Tolkien"

hobbit.year
# => 1937

hobbit.title
# => "The Hobbit"

Bracket Notation + Positional arguments

Location = Data.define(:latitude, :longitude)
# => Location

We can use positional arguments but need to take care with the order.

philadelphia = Location[39.9526, -75.1652]
# => #<data Location latitude=39.9526, longitude=-75.1652>

philadelphia.latitude
# => 39.9526

philadelphia = Location[-75.1652, 39.9526]
# => #<data Location latitude=-75.1652, longitude=39.9526>

philadelphia.latitude
# => -75.1652

Bracket Notation + Keyword Arguments

Note that with keyword arguments, we have flexibility in the order we pass arguments.

philadelphia = Location[latitude: 39.9526, longitude:-75.1652]
# => #<data Location latitude=39.9526, longitude=-75.1652>

philadelphia.latitude
# => 39.9526

philadelphia = Location[longitude:-75.1652, latitude: 39.9526]
# => #<data Location latitude=39.9526, longitude=-75.1652>

philadelphia.latitude
# => 39.9526

What is Ruby's Data class?

Create the blueprint (instance of Data class)

Building from the blueprint

.new + keyword arguments

Bracket Notation + Positional arguments

Bracket Notation + Keyword Arguments

Further Reading

Related Posts

`.new` + keyword arguments