irb(main):001:0> class Foo;class << self; attr_reader :bar;def bar=(val) print "in bar"; @bar=val end end end
=> :bar=
irb(main):002:0> Foo.bar
=> nil
irb(main):003:0> Foo.bar={}
in bar=> {}
irb(main):004:0> Foo.bar
=> {}
irb(main):005:0> Foo.bar['a']='b'
=> "b"
irb(main):006:0> Foo.bar
=> {"a"=>"b"}