perl语言中定义枚举变量和C语言中类似，默认都是从0开始，并依次递增1个单位；
也可以重新自定义枚举变量的起始值，示例如下：
定义枚举变量：
use enum qw(Sun Mon Tue Wed Thu Fri Sat);
# Sun == 0,Mon == 1,etc
use enum qw(Forty=40 FortyOne Five=5 Six Seven);
# Yes,you can change the start indexs at any time as in C
use enum qw(:Prefix_ One Two Three);
## Creates Prefix_One,Prefix_Two,Prefix_Three
use enum qw(:Letters_ A..Z);
## Creates Letters_A,Letters_B,Letters_C,...
use enum qw( :Months_=0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec :Days_=0 Sun Mon Tue Wed Thu Fri Sat );
测试代码：
print "enum Wed val: ",Wed,"\n" ;
print "enum FortyOne val: ",FortyOne,"\n" ;
print "enum Prefix_Two val: ","\n" ;
print "enum Letters_A val: ",Letters_A,"\n" ;
print "enum Months_Jan val: ",Months_Jan,"\n" ;
print "enum Days_Sun val: ",Days_Sun,"\n" ;
测试结果：
enum Wed val: 3
enum FortyOne val: 41
enum Prefix_Two val: 1
enum Letters_A val: 0
enum Months_Jan val: 0
enum Days_Sun val: 0
更多参考资料：
https://metacpan.org/pod/enum
