Class Attribute test

class_attribute_test.rb

require 'active_support/all'

class A
  class_attribute :attrs
  self.attrs = {}
end

class B < A
end

class C < A
end

def puts_attrs(desc)
  puts desc
  puts A.attrs
  puts B.attrs
  puts C.attrs
end

puts_attrs 'Unset'
A.attrs[:a] = 1
puts_attrs 'A []='
A.attrs.merge!(b: 2)
puts_attrs 'A merge!'
A.attrs = A.attrs.merge(c: 3)
puts_attrs 'A =merge'
B.attrs[:x] = 1
puts_attrs 'B []='
B.attrs.merge!(y: 2)
puts_attrs 'B merge!'
B.attrs = B.attrs.merge(z: 3)
puts_attrs 'B = merge'

=begin # output
$ ruby class_attribute_test.rb
Unset
{}
{}
{}
A []=
{:a=>1}
{:a=>1}
{:a=>1}
A merge!
{:a=>1, :b=>2}
{:a=>1, :b=>2}
{:a=>1, :b=>2}
A =merge
{:a=>1, :b=>2, :c=>3}
{:a=>1, :b=>2, :c=>3}
{:a=>1, :b=>2, :c=>3}
B []=
{:a=>1, :b=>2, :c=>3, :x=>1}
{:a=>1, :b=>2, :c=>3, :x=>1}
{:a=>1, :b=>2, :c=>3, :x=>1}
B merge!
{:a=>1, :b=>2, :c=>3, :x=>1, :y=>2}
{:a=>1, :b=>2, :c=>3, :x=>1, :y=>2}
{:a=>1, :b=>2, :c=>3, :x=>1, :y=>2}
B = merge
{:a=>1, :b=>2, :c=>3, :x=>1, :y=>2}
{:a=>1, :b=>2, :c=>3, :x=>1, :y=>2, :z=>3}
{:a=>1, :b=>2, :c=>3, :x=>1, :y=>2}
=end