Typeglobs typeglob 引用檔案控制代碼和常量
typeglob *foo
儲存對具有該名稱的全域性變數內容的引用 :$foo
,@foo
,$foo
,&foo
等。你可以像雜湊一樣訪問它並指定直接操作符號表(邪惡!)。
use v5.10; # necessary for say
our $foo = "foo";
our $bar;
say ref *foo{SCALAR}; # SCALAR
say ${ *foo{SCALAR} }; # bar
*bar = *foo;
say $bar; # bar
$bar = 'egg';
say $foo; # egg
處理檔案時更常處理 Typeglobs。例如,當要求建立非全域性檔案控制代碼時,open
會生成對 typeglob 的引用:
use v5.10; # necessary for say
open(my $log, '> utf-8', '/tmp/log') or die $!; # open for writing with encoding
say $log 'Log opened';
# You can dereference this globref, but it's not very useful.
say ref $log; # GLOB
say (*{$log}->{IO} // 'undef'); # undef
close $log or die $!;
Typeglobs 也可用於製作全域性只讀變數,但 use constant
可以廣泛使用。
# Global constant creation
*TRUE = \('1');
our $TRUE;
say $TRUE; # 1
$TRUE = ''; # dies, "Modification of a read-only value attempted"
# use constant instead defines a parameterless function, therefore it's not global,
# can be used without sigils, can be imported, but does not interpolate easily.
use constant (FALSE => 0);
say FALSE; # 0
say &FALSE; # 0
say "${\FALSE}"; # 0 (ugh)
say *FALSE{CODE}; # CODE(0xMA1DBABE)
# Of course, neither is truly constant when you can manipulate the symbol table...
*TRUE = \('');
use constant (EVIL => 1);
*FALSE = *EVIL;