hanleilei

#这个问题解决了：
#Most of the power comes from the implicit smartmatching
#that can sometimes apply. Most of the time, when(EXPR) is
#treated as an implicit smartmatch of $_ , that is, $_ ~~ EXPR .
#(See Smartmatch Operator in perlop for more information on smartmatching.)
#But when EXPR is one of the 10 exceptional cases 
#(or things like them) listed below, it is used directly as a boolean.

#1.  A user-defined subroutine call or a method invocation.
#其他省略