perl – 无论如何,都会认为字符串重载变量已定义

如果是这种情况,那么在检查它是否被定义之前,您需要将其强制转换为String形式：

if (! defined overload::StrVal($spec)) {

每月更正

正如在StrVal中指出的那样,没有强制重载的字符串化：

overload::StrVal(arg)

Gives the string value of arg as in the absence of stringify overloading. If you are using this to get the address of a reference (useful for checking if two references point to the same thing) then you may be better off using Scalar::Util::refaddr(),which is faster.

因此,要实现这一点,请尝试他的另一个建议：

“$spec” trapping warnings and detecting the uninitialized var warning. Better to add a method to the class to test for whatever case returns undef.

以下演示了这种方法：

#!/usr/bin/env perl

use strict;
use warnings;

use Test::More tests => 2;

my $obj_str_defined = StringOverloaded->new("has value");
my $obj_str_undef   = StringOverloaded->new(undef);

ok( is_overloaded_string_defined($obj_str_defined),qq{$obj_str_defined is defined} );
ok( !is_overloaded_string_defined($obj_str_undef),qq{$obj_str_undef is undef} );

sub is_overloaded_string_defined {
    my $obj = shift;

    my $is_str_defined = 1;

    local $SIG{__WARN__} = sub {
        $is_str_defined = 0 if $_[0] =~ /Use of uninitialized value $obj in string/;
    };

    my $throwaway_var = "$obj";

    return $is_str_defined;
}

{
    # Object with string overloading
    package StringOverloaded;

    use strict;
    use warnings;

    use overload (
        '""' => sub {
            my $self = shift;
            return $$self;    # Dereference
        },fallback => 1
    );

    sub new {
        my $pkg  = shift;
        my $val  = shift;
        my $self = bless $val,$pkg;

        return $self;
    }
}

输出：

1..2
ok 1 - $obj_str_defined is defined
ok 2 - $obj_str_undef is undef