一个关于typeglob的诡异问题，求教

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1. #!/usr/bin/perl -w
   
2. use 5.010;
   
3. use strict;
   
4. 
   
5. our $foo = 'foo';
   
6. my $k = *foo;
   
7. 
   
8. ${*{*{*{$k}}}} = 'k';
   
9. say $foo;
   
10. ${*{*{*{*foo}}}} = 'glob';
    
11. say $foo;
    
12. *{*{*{*{$k}}}} = \'k2';
    
13. say $foo;
    
14. *{*{*{*{*foo}}}} = \'glob2';
    
15. say $foo;

复制代码

输出：
k
glob
glob
glob2

第一种方式的赋值，无论是用$k还是*foo都能成功，但第二种方式的赋值，用$k却无法起效（但是也无警告不报错）

查了许多资料依然没找到为什么，请知道的人说下，多谢

兰花仙子

没太多意义的写法。
知道 *foo 与 *{*foo} 是一个东西就明了。

zhlong8

5.14 下好像不大一样啊，我的是
k
glob
k2
glob2

实现不懂 *{*k} 有什么意义就查了下文档，在 perlref 中

A typeglob may be dereferenced the same way a reference can, because the dereference syntax always indicates the type of reference desired. So ${*foo} and ${\$foo} both indicate the same scalar variable.

也就是说 *{*foo} 外面的 * 需要里面是一个 typeglob 引用，所以里面的 typeglob 会当做 typeglob 的引用来处理，即 *{*foo} === *foo。因为对 typeglob 解引用逻辑上没什么意义这里应该算是约定。

所以，第一个 ${*{*{*{$k}}}} = 'k'; 等于 ${*{*{*{*foo}}}} = 'k' 等于 ${*foo} = 'k'; 等于 $foo = 'k';
第二个 ${*{*{*{*foo}}}} = 'glob'; 同上
第三个*{*{*{*{$k}}}} = \'k2'; 等于 *{*{*{*{*foo}}}} = \'k2';  等价于 *foo = \'k2';
第四个 *{*{*{*{*foo}}}} = \'glob2'; 同上一个，等价于 *foo = \'glob2';

twilightagain

回复 3# zhlong8


    多谢3楼的解答。

手头是5.12版本的，确实和我在主楼写的显示一样，然后去翻了下5.12-5.14的升级，终于找到了问题：

Some Perl operators did not distinguish between these two types of globs. This would result in strange behaviour in edge cases: untie $scalar would not untie the scalar if the last thing assigned to it was a glob (because it treated it as untie *$scalar , which unties a handle). Assignment to a glob slot (such as *$glob = \@some_array ) would simply assign \@some_array to $glob .

原文链接：http://perldoc.perl.org/5.14.0/perldelta.html#Selected-Bug-Fixes

标量和其中存储的typeglob的行为区别是一个bug，现在已经修复：

To fix this, the *{} operator (including its *foo and *$foo forms) has been modified to make a new immutable glob if its operand is a glob copy. This allows operators that make a distinction between globs and scalars to be modified to treat only immutable globs as globs. (tie, tied and untie have been left as they are for compatibility's sake, but will warn. See Deprecations.)