gistfile1.txt

pry(main):1> class Foo; attr_writer :bar; end                                                                          
=> nil
pry(main):2> x = Foo.new                                                                                               
=> #<Foo:0x46040d8>
pry(main):3> x.bar ||= 3 # errors                                                                                      
NoMethodError: undefined method `bar' for #<Foo:0x000000046040d8>
  from (pry):3:in `__pry__'
pry(main):4> (x.bar = x.bar if defined?(x.bar)) || x.bar = 3 # no error                                                
=> 3