perl goto的不同用法

redskywy

先看一下官方的文档

The goto-&NAME  form is quite different from the other forms of goto. In fact, it isn't a goto in the normal sense at all, and doesn't have the stigma associated with other gotos. Instead, it exits the current subroutine (losing any changes set by local()) and immediately calls in its place the named subroutine using the current value of @_. This is used by AUTOLOAD  subroutines that wish to load another subroutine and then pretend that the other subroutine had been called in the first place (except that any modifications to @_ in the current subroutine are propagated to the other subroutine.) After the goto, not even caller will be able to tell that this routine was called first.

goto &subname 是先退出当前的过程然后执行 过程 subname,这样可以避免在使用 return subname 的时候在subname内部使用受到影响的一些变量
如：

1. 
   
2. sub test1 {
   
3.      print "This is test1 ";
   
4.      print "\$/ is:" . $/;
   
5. }
   
6. sub test2 {
   
7.        local $/ = '#';
   
8.        goto &test1;
   
9. }
   
10. sub test3 {
    
11.        local $/ = '#';
    
12.        return test1();
    
13. }
    
14. print "call test2\n";
    
15. test2();
    
16. print "\ncall test3\n";
    
17. test3();
    

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在查看 Export.pm模块时发现这个比较特殊的用法，感觉很好很强大

1. 
   
2. sub export {
   
3.   goto &{as_heavy()};
   
4. }
   

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dugu072_cu

AUTOLOAD 就是利用 goto 实现的 proxy 效果