perl – 为什么要使用警告？去最后？

我模糊地回顾,警告的pragma应该在我们正在加载使用的模块的列表中最后.我也模糊地记得,它与模块注册自己的警告类别有关,但我无法重现任何问题.有人可以指向相关文章,还是显示一个示例,其中警告标注的位置有何区别？

解决方法

这可能是你所指的.无论哪种方式,都需要注意,我将其作为一个错误提交

我/ Warnings.pm

package My::Warnings;

use warnings::register;

sub test {
    warnings::warnif 'This is my warning';
}

1;

main.pl

use strict;
use feature 'switch';

use warnings 'all';

use My::Warnings;

print undef;

given (1) { }

My::Warnings::test();

如预期的那样,这将产生

given is experimental at E:\Perl\source\main.pl line 10.
Use of uninitialized value in print at E:\Perl\source\main.pl line 8.
This is my warning at E:\Perl\source\main.pl line 12.

但是,如果任何警告类别被禁用,它也将禁用自定义类别.喜欢这个

use strict;
use feature 'switch';

use warnings 'all';
no warnings 'experimental';

use My::Warnings;

print undef;

given (1) { }

My::Warnings::test();

这只输出

Use of uninitialized value in print at E:\Perl\source\main.pl line 9.

并且似乎有必要在使用My :: Warnings之后启用警告以使其执行

use strict;
use feature 'switch';

use My::Warnings;

use warnings 'all';
no warnings 'experimental';

print undef;

given (1) { }

My::Warnings::test();

产生

Use of uninitialized value in print at E:\Perl\source\main.pl line 9.
This is my warning at E:\Perl\source\main.pl line 13.

更新

此外,重新启用关闭自定义警告的类别会使其被禁用

这样的东西

use strict;
use feature 'switch';

use warnings 'all';
no warnings 'experimental';
use warnings 'experimental';

use My::Warnings;

print undef;

given (1) { }

My::Warnings::test();

打印

given is experimental at E:\Perl\source\main.pl line 12.
Use of uninitialized value in print at E:\Perl\source\main.pl line 10.