Perl 的模板工具包可以对未定义的值发出警告吗？

发布于 2024-07-13 22:08:07 字数 325 浏览 7 评论 0原文

有没有办法让 Perl 的 Template 对我尝试使用 GET 指令（通过 [% %]）在 模板::流程？

默认行为是忽略并继续。如果可能的话，我想仅在未定义值的情况下发出警告，并将消息记录到 STDERR。

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这样的小城市 2024-07-20 22:08:07

您正在寻找：

DEBUG_UNDEF

此选项会导致模板工具包在遇到未定义的变量值时抛出“undef”错误。

use Template::Constants qw( :debug );

my $template = Template->new({
    DEBUG => DEBUG_UNDEF,
});

（来自 http://search.cpan.org/ dist/Template-Toolkit/lib/Template/Manual/Config.pod。）

如果你想对异常进行一些特殊处理，你需要捕获它或替换 __DIE__ 信号处理程序。

让我们把它们放在一起：

#!/usr/bin/perl

use strict;
use warnings;

use Template;
use Template::Constants qw( :debug );

my $debug_tt = Template->new({
   DEBUG => DEBUG_UNDEF,
});

my $tt = Template->new();

my $vars = {
    something => "42",
};

my $template = <<EOF;
First something undefined: [% nothing %].
And now something defined: [% something %].
EOF

my $output = '';

eval {$debug_tt->process(\$template, $vars, \$output)};
warn $debug_tt->error() if $debug_tt->error();

$tt->process(\$template, $vars);

输出是：

undef error - nothing is undefined
First something undefined: .
And now something defined: 42.

我的方法是使用 Template 类的两个不同实例：

$debug_tt ，其中打开并隐藏了 DEBUG_UNDEF 标志它的输出位于 $output 变量中。
$tt 这是一个普通实例，默认情况下将其输出打印到 STDOUT。

两个实例都使用存储在 $template 中的相同模板以及存储在 $vars 中的相同变量哈希。 $debug_tt 包装在 eval 中以避免过早退出，如果 $debug_tt->error() 为 true，则会发出警告。 $tt 正常执行。我认为这满足了您的主要要求，尽管它可能效率不高。我们需要使用此方法解析 $template 两次。

我对此的一些想法：

如果 Template::Toolkit 使用 Carp 那就太好了，这样我们就可以获得有关警告的更多背景信息.
人们可能可以从 Template 派生一个类，该类会在出错时发出警告而不是死亡。我不想这样做。
根据模板的设置方式，一次输入一行可能是有意义的，这样您就可以在发现未定义的值时发出行号。
应该可以更改模板来测试自己的错误，并在面对未定义的值时发出更明智的文本。
应该可以更改

You are looking for:

DEBUG_UNDEF

This option causes the Template Toolkit to throw an 'undef' error whenever it encounters an undefined variable value.

use Template::Constants qw( :debug );

my $template = Template->new({
    DEBUG => DEBUG_UNDEF,
});

(From http://search.cpan.org/dist/Template-Toolkit/lib/Template/Manual/Config.pod.)

If you want to do some special handling of the exception, you'll need to catch it or replace the __DIE__ signal handler.

Let's put it together:

#!/usr/bin/perl

use strict;
use warnings;

use Template;
use Template::Constants qw( :debug );

my $debug_tt = Template->new({
   DEBUG => DEBUG_UNDEF,
});

my $tt = Template->new();

my $vars = {
    something => "42",
};

my $template = <<EOF;
First something undefined: [% nothing %].
And now something defined: [% something %].
EOF

my $output = '';

eval {$debug_tt->process(\$template, $vars, \$output)};
warn $debug_tt->error() if $debug_tt->error();

$tt->process(\$template, $vars);

The output is:

undef error - nothing is undefined
First something undefined: .
And now something defined: 42.

My approach was to use two different instances of the Template class:

$debug_tt which has the DEBUG_UNDEF flag turned on and hides its output in the $output variable.
$tt which is a vanilla instance and prints its output to STDOUT as is the default.

Both instances use the same template stored in $template and the same variable hash stored in $vars. $debug_tt is wrapped in an eval to avoid exiting prematurely and a warning is emitted if $debug_tt->error() is true. $tt is executed normally. I think this satisfies your main requirements although it probably isn't efficient. We need to parse $template twice using this method.

Some thoughts I had working on this:

It would have been nice if Template::Toolkit had used Carp so that we could get a bit more context on the warning.
One could probably derive a class from Template that would warn instead of die on error. I didn't feel like doing that.
Depending on how your templates are set up, it might make sense to feed it in one line at a time so that you could emit line numbers when an undefined value is found.
It should be possible to alter the templates to test for their own errors and emit more sensible text in the face of undefined values.