防止将字符串解释为文件句柄 [英] Prevent strings from being interpreted as a file handle

问题描述

Perl具有将名为文件句柄的字符串用作 文件句柄的功能:

Perl has the feature that strings named like a file handle are taken to be a filehandle:

# let this be some nice class I wrote
package Input {
    sub awesome { ... }
}

因此，当我们执行Input->awesome或格外小心时:'Input'->awesome，该方法将被调用.除非:

So when we do Input->awesome or extra-careful: 'Input'->awesome, the method will get called. Unless:

# now somewhere far, far away, in package main, somebody does this:
open Input, "<&", \*STDIN or die $!;  # normally we'd open to a file

甚至不必执行此代码，而只是为了使Perl从现在开始使Perl将字符串'Input'解释为文件句柄，解析器才能看到.因此，方法调用'Input'->awesome将死亡，因为代表文件句柄的对象没有很棒的方法.

This code doesn't even have to be executed, but only be seen by the parser in order to have Perl interpret the string 'Input' as a file handle from now on. Therefore, a method call 'Input'->awesome will die because the object representing the file handle doesn't have awesome methods.

由于我只能控制类，而不能控制其他代码，所以我不能简单地决定只在各处使用词法文件句柄.

As I am only in control of my class but not of other code, I can't simply decide to only use lexical filehandles everywhere.

有什么办法可以强制Input->awesome始终是Input程序包上的方法调用，但从来没有文件句柄(至少在我控制的范围内)?我认为不应有任何名称冲突，因为Input包实际上是%Input::藏匿处.

Is there any way I can force Input->awesome to always be a method call on the Input package, but never a file handle (at least in scopes controlled by me)? I'd think there shouldn't be any name clash because the Input package is actually the %Input:: stash.

重现该问题的完整代码(另请参见此 ideone ):

Full code to reproduce the problem (see also this ideone):

use strict;
use warnings;
use feature 'say';

say "This is perl $^V";

package Input {
    sub awesome {
        say "yay, this works";
    }
}

# this works
'Input'->awesome;

# the "open" is parsed, but not actually executed
eval <<'END';
    sub red_herring {
        open Input, "<&", \*STDIN or die $!;
    }
END
say "eval failed: $@" if $@;

# this will die
eval {
    'Input'->awesome;
};
say "Caught: $@" if $@;

示例输出:

This is perl v5.16.2
yay, this works
Caught: Can't locate object method "awesome" via package "IO::File" at prog.pl line 27.

推荐答案

对于两个不同的事物(使用的类和文件句柄)使用相同的标识符会引起问题.如果您的类是从使用文件句柄的代码中使用的其他类中使用的，则不会出现该错误:

Using the same identifier for two different things (a used class and filehandle) begs for problems. If your class is used from a different class that's used in the code that uses the filehandle, the error does not appear:

package My1;

use warnings;
use strict;

sub new { bless [], shift }
sub awesome { 'My1'->new }

__PACKAGE__

My2.pm

package My2;

use warnings;
use strict;
use parent 'My1';

sub try {
    my $self = shift;
    return ('My1'->awesome, $self->awesome);
}

__PACKAGE__

script.pl

#!/usr/bin/perl
use warnings;
use strict;

use My2;
open My1, '<&', *STDIN;
my $o = 'My2'->new;
print $o->awesome, $o->try;

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