dry_types_struct_w_subclasses.rb

require 'bundler/inline'
gemfile true do
  gem 'dry-types'
end

include Dry::Types.module

class A < Dry::Types::Struct
  attribute :a, Strict::Int
end

class AA < A
  attribute :aa, Strict::Int
end

class AB < A
  attribute :ab, Strict::Int
end

class Foo < Dry::Types::Struct
  attribute :bar, A
end


a = A.new(a: 123)
aa = AA.new(a: 123, aa: 234)
ab = AB.new(a: 123, ab: 345)

foo = Foo.new(bar: a)
p [ foo.bar.class,
    foo.bar.is_a?(A),
    foo.bar.is_a?(AA),
    foo.bar.is_a?(AB) ]
# [A, true, false, false]
# everything as expected

foo = Foo.new(bar: aa)
p [ foo.bar.class,
    foo.bar.is_a?(A),
    foo.bar.is_a?(AA),
    foo.bar.is_a?(AB) ]
# [A, true, false, false]
# hmm the type checking worked with subclasses
# but the attribute got somehow coerced? typecasted? type-assigned to it's parent class

foo = Foo.new(bar: ab)
p [ foo.bar.class,
    foo.bar.is_a?(A),
    foo.bar.is_a?(AA),
    foo.bar.is_a?(AB) ]
# [A, true, false, false]
# same as with AA