Lab42::DataClass

A dataclass with an immutable API (you can still change the state of the object with metaprogramming and lab42_immutable is not ready yet!)

Usage

gem install lab42_data_class

With bundler

  gem 'lab42_data_class'

In your code

require 'lab42/data_class'

So what does it do?

Well let us speculate about it to find out:

Context: DataClass function

Given

    let(:my_data_class) { DataClass(:name, email: nil) }
    let(:my_instance) { my_data_class.new(name: "robert") }

Then we can access its fields

    expect(my_instance.name).to eq("robert")
    expect(my_instance.email).to be_nil

But we cannot access undefined fields

    expect{ my_instance.undefined }.to raise_error(NoMethodError)

And we need to provide values to fields without defaults

    expect{ my_data_class.new(email: "some@mail.org") }
      .to raise_error(ArgumentError, "missing initializers for [:name]")

And we can extract the values

    expect(my_instance.to_h).to eq(name: "robert", email: nil)

Context: Immutable

Given

    let(:other_instance) { my_instance.merge(email: "robert@mail.provider") }

Then we have a new instance with the old instance unchanged

    expect(other_instance.to_h).to eq(name: "robert", email: "robert@mail.provider")
    expect(my_instance.to_h).to eq(name: "robert", email: nil)

Context: Defining behavior with blocks

Given

    let :my_data_class do
      DataClass :value, prefix: "<", suffix: ">" do
        def show
          [prefix, value, suffix].join
        end
      end
    end
    let(:my_instance) { my_data_class.new(value: 42) }

Then I have defined a method on my dataclass

    expect(my_instance.show).to eq("<42>")

Context: Making a dataclass from a class

Given

    class DC
      dataclass x: 1, y: 41
      def sum; x + y end
    end

Then we can define methods on it

   expect(DC.new.sum).to eq(42)

And we have a nice name for our instances

    expect(DC.new.class.name).to eq("DC")

LICENSE

Copyright 2022 Robert Dober robert.dober@gmail.com

Apache-2.0 c.f LICENSE