This is part 1 in this series on Ruby's Data Class. Part 2 compares Data with Struct. Part 3 explores immutability workarounds with Data.
What is the Data class?
A Ruby class to allow the definition of simple classes for value-alike objects.
Data is intended to store immutable values*.
Once defined, its instance cannot
*A future post will explore the wiggle room here.
Once defined, the instance of Data class is
A Ruby class designed to create for objects with the intention of being immutable.
The Data class was introduced to Ruby in Ruby 3.2, to:
- 'define simple classes for value-alike'
- store immutable atomic values
When was Data brought into Ruby?
Ruby 3.2
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
.newor 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
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