perl – 安全隔间中的“无警告”

例如,以下代码：

use strict; use warnings;
use Safe;    
use feature qw/say/;
my $cft = Safe->new;

my $x = $cft->reval(') 1' );
my $y = $cft->reval('2'   );
say "x: $x";
say "y: $y";

结果是：

Number found where operator expected at (eval 5) line 1,near ") 1"
    (Missing operator before 1?)
Use of uninitialized value $x in concatenation (.) or string at ./test line 12.
x: 
y: 2

我想要实现的是$x = undef和$y = 2,没有警告.
我试图提出“没有警告;”在新范围内,但它对reval中产生的警告没有影响(尽管如@DavidO指出的那样,它会使’未初始化值’警告静音)：

use strict; use warnings;
use Safe;    
use feature qw/say/;
my $cft = Safe->new;
{
    no warnings;
    my $x = $cft->reval(') 1' );
    my $y = $cft->reval('2'   );
    say "x: $x";
    say "y: $y";
}

我想不管怎么说’没有警告’必须在安全隔间内,所以我也尝试在“没有警告”前面加上被评估的字符串：

use strict; use warnings;
use Safe;
use feature qw/say/;
my $cft = Safe->new;
{
    my $x = $cft->reval( 'no warnings;' . ') 1' );
    my $y = $cft->reval( 'no warnings;' . '2'   );
    say "x: $x";
    say "y: $y";
}

这种方式reval不会发出任何警告,但两个变量都是undef：

Use of uninitialized value $x in concatenation (.) or string at ./test line 10.
x: 
Use of uninitialized value $y in concatenation (.) or string at ./test line 11.
y:

我不知道还有什么可以尝试,我希望问题描述足够清楚.