perl - "no autovivication"杂注在 Perl 中使用 grep 失败

Question

我正在尝试使用以下模块关闭自动恢复:https://metacpan.org/pod/autovivification但 grep 失败了:

#!/usr/bin/env perl

use strict;
use warnings FATAL => 'all';
use feature 'say';
use autodie ':all';
use DDP;
no autovivification;

my %h = (
    'a' => 1,
    'b' => 2,
);
p %h; # pretty print the original hash
my @fake_keys = ('x', 'y', 'z');
if (grep {defined} @h{@fake_keys}) {
    say "found fake keys";
}
p %h; # show that 'x', 'y', & 'z' are added as undef keys

如何关闭 grep 的自动激活？

Answer 1

这不是 grep但是导致这种情况的哈希片中的值的别名。
这具有相同的效果:

for (@h{@fake_keys}){
 my $t = $_;
}

您可以通过复制切片来解决它:

use strict;
use warnings FATAL => 'all';
use feature 'say';
use autodie ':all';
use DDP;

my %h = (
    'a' => 1,
    'b' => 2,
);
p %h; # pretty print the original hash
my @fake_keys = ('x', 'y', 'z');
if (grep {defined} @{[@h{@fake_keys}]}) {
    say "found fake keys";
}
p %h; # show that 'x', 'y', & 'z' are added as undef keys

或者访问 grep block 中的每个值，例如 shown池上.