特定
# package main;
our $f;
sub f{}
sub g {}
1;
如何确定已声明$f而非$g？关闭袖口,我认为* {main :: g} {SCALAR}可能是未定义的,但它是一个真正的SCALAR参考.
背景：我想将变量导入main ::,但是如果已经声明了该变量,则将carp或croak导入.
编辑添加了一个f子程序来响应@ DVK的初始答案.
答案(2010-07-27)
这并不容易,但有可能.
eval technique是最便携的,工作在早于5.10的perls上.在最近的perls中,内省模块如Devel::Peek和B可以区别对待.
解决方法
我尽我所能,甚至试图询问eval STRING是否已经通过我们或我的声明$main :: f. (这需要重复,关闭,以及稍后恢复STDERR以减少干扰.)一旦你更改了包,那些临时转回的声明就不再可见了.
下面的技术将检测是否已通过声明$f
use vars qw/ $f /;
代码如下：
package MyModule;
use warnings;
use strict;
# using $f will confuse the compiler,generating
# warnings of 'Variable "%f" is not available'
# although we're going for $main::f
my $__f = "from MyModule";
my %IMPORT_OK = (
'$f' => [f => \$__f],);
sub import {
my($pkg,@imports) = @_;
my $callpkg = caller;
die "I don't speak your dirty Pig-Latin"
if $callpkg !~ /\A\w+(::\w+)*\z/ ||
grep !/\A[\$@%]\w+\z/,@imports;
foreach my $name (@imports) {
my($sym,$ref) = @{ $IMPORT_OK{$name} || [] };
die "unknown import: $name" unless $sym;
open my $saverr,">&",\*STDERR or die "dup STDERR: $!";
close STDERR;
my $declared = eval qq{
package $callpkg;
my(undef)=$name;
1;
};
open STDERR,$saverr or print "restore STDERR: $!";
die "${callpkg}::$sym already exists" if $declared;
{
no strict 'refs';
*{$callpkg . "::" . $sym} = $ref;
}
}
}
1;