my $spec = shift;
if (!defined $spec) {
return ("Invalid specification",undef);
}
$spec = "$spec" // '';
我自然希望这会在传递undef时返回数组中的警告Invalid specification,第二项是undef.相反,检查通过,我得到一个控制台消息警告我在下一行使用未初始化的值$spec in string.
$spec是一个带字符串和数字重载的对象,不幸的是这样编写,试图在这个特定的子例程中测试真实性(例如if($spec))会导致深度递归和段错误.
虽然我感兴趣的是,为什么,确切地说,这种情况正在发生,但我更感兴趣的是如何让它停止发生.我想消除控制台警告,最好没有警告qw / uninitialized /.这是可能的,如果是的话,我该怎么做？
解决方法
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