perl - 警告 : something's wrong when ref $body->param->{aa}

Question

我正在测试 HTTP::Body,

然后

my $body = HTTP::Body->new($ct, $cl);
#..
use Data::Dumper;
warn Dumper($body);                  #A
warn ref $body;                      #B
warn Dumper($body->param);           #C
warn ref $body->param;               #D
warn Dumper($body->param->{aa});     #E
warn ref $body->param->{aa};         #F

输出:

#A
$VAR1 = bless( {
                 'param_order' => [
                                    'aa',
                                    'bb'
                                  ],
                 'param' => {
                              'aa' => 'b',
                              'bb' => 'a',
                            },
                 'cleanup' => 1
               }, 'HTTP::Body::MultiPart' );
#B
HTTP::Body::MultiPart at
#C
$VAR1 = {
          'aa' => 'b',
          'bb' => 'a',
        };
#D
HASH at 
#E
$VAR1 = 'b';
#F
Warning: something's wrong at 

为什么 Warning: somethings wrong, $body->param->{aa} 不是 STRING？如何使其成为字符串？

Answer 1

something's wrong 是 warn 函数在接收到空字符串或没有输入时输出的默认消息。

$ perl -e warn
Warning: something's wrong at -e line 1.

$ perl -e 'warn ""'
Warning: something's wrong at -e line 1.

$ perl -e '$body={param=>{aa=>"b"}};warn ref($body->{param}{aa})'
Warning: something's wrong at -e line 1.

我想您也对 ref 对普通标量(例如字符串)的作用感到困惑。如果 ref 的输入不是引用，则输出为空字符串。

print ref(42);                 # no output
print ref(undef);              # no output
$foo="abc"; print ref($foo);   # no output
warn ref($foo);                # like warn "", so "something's wrong"