Creates struct-like classes (that can build value objects) that do not have setters and also have better constructors than Ruby's built-in Struct.
This is highly useful for creating presenters, non-database-related models, or other quick and dirty classes in your application. Instead of using a Hash or OpenStruct, you can create a bit more clarity around your types by using ImmutableStruct, which is almost as convienient.
Add to your Gemfile:
If not using bundler, just use RubyGems:
gem install immutable-struct
Person = ImmutableStruct.new(:name, :age, :job, :active?, [:addresses]) do def minor? age < 18 end end p = Person.new(name: "Dave", # name will be 'Dave' age: 40, # age will be 40 # job is omitted, so will be nil active: true) # active and active? will be true # addresses is omitted, but since we've selected # Array coercion, it'll be  p.name # => "Dave" p.age # => 40 p.active? # => true p.minor? # => false p.addresses # =>  p2 = Person.new(name: "Dave", age: 40, active: true) p == p2 # => true p.eql?(p2) # => true SimilarPerson = ImmutableStruct.new(:name, :age, :job, :active?, [:addresses]) sp = SimilarPerson.new(name: "Dave", age: 40, active: true) p == sp # => false # Different class leads to inequality new_person = p.merge(name: "Other Dave", age: 41) # returns a new object with merged attributes new_person.name # => "Other Dave" new_person.age # => 41 new_person.active? # => true
You can treat the interior of the block as a normal class definition with the exception of setting constants. Use const_set to scope constants as-expected.
Point = ImmutableStruct.new(:x, :y) do const_set(:ZERO, 0) ONE_HUNDRED = 100 end Point::ZERO # => 0 ::ONE_HUNDRED # => 100 ::ZERO # => NameError: uninitialized constant ZERO