e$B0J2<$N$h$&$K!"e(B@a?, @a! e$B$,%$%s%9%?%s%9JQ?t$H$5$l$k$N$OJQ$G$Oe(B
e$B$J$$$G$7$g$&$+!#e(B
% ./ruby -ve ‘@a = “x”; p “[#@a?][#@a!]”’
ruby 1.9.0 (2008-05-02 revision 16286) [i686-linux]
-e:1: warning: instance variable @a? not initialized
-e:1: warning: instance variable @a! not initialized
“[][]”