我应该在哪里捕获Perl 6警告控制异常？ [英] Where should I catch a Perl 6 warning control exception?

问题描述

我正在研究Perl 6的控件异常。 warn 引发一个控制异常，该异常对于正常的异常控制流是不可见的，并且该异常会自行恢复。挺酷的

I'm playing around with Perl 6's control exceptions. A warn raises a control exception which is invisible to normal exception control flow, and that exception resumes itself. That's kinda cool.

所以，我玩这个，看看会发生什么。除了查看Perl 6的实际功能外，我没有尝试解决特定的问题：

So, playing around with this, I wrote this to see what would happen. I'm not trying to solve a particular problem other than seeing what Perl 6 actually does:

use v6;

try {
    CONTROL {
        put "Caught an exception, in the try";
        put .^name;
        }
    do-that-thing-you-do();
    }

sub do-that-thing-you-do {
    CONTROL {
        put "Caught an exception, in the sub";
        put .^name;
        }
    warn "This is a warning";
    }

看起来像是两堆火：

Caught an exception, in the sub
CX::Warn
Caught an exception, in the try
CX::Warn
This is a warning
  in sub do-that-thing-you-do at resume.p6 line 16
MoarVM panic: Trying to unwind over wrong handler

请注意，这里有一场恐慌恐慌，我提出了一个问题。但是，我并不是真的在问这个。

Notice there's a Moar panic, which I've raise an issue for. But, I'm not really asking about that.

我很好奇这里的流程。我希望子对象中的 CONTROL 会捕获异常并继续运行，因此它不会渗透到 try 。

I'm curious about the picture of the flow here. I expected that a CONTROL in the sub would catch the exception and resume, so it wouldn't percolate up to the try. How should that flow?

另外，请注意，例外是 CX :: Warn 。我认为我在这里所做的事情并不奇怪，但是 Perl 6类型却没有甚至列出 X :: Warn

Also, notice the exception is CX::Warn. I don't think I've done something odd there, but the Perl 6 types don't even list X::Warn

推荐答案

要获得与默认的警告处理程序，那么有必要同时捕获异常（例如 CATCH ， CONTROL ，而无需智能匹配）将会重新抛出），并且在恢复后也恢复为 。

To get the same behavior as the default warnings handler, then it's necessary to both catch the exception (as with CATCH, a CONTROL without smart-matching will re-throw) and also to resume after it.

CONTROL {
    when CX::Warn {
        say "Warning: $_";
        .resume
    }
}

sub foo() {
    say 1;
    warn 'oh gosh...';
    say 2;               # Not reached without .resume
}
foo();

还有许多其他控制例外，因此明智的做法是只匹配 CX :: Warn 而不是使用 default 。否则，获取，下一步，最后， emit ， done （在6.d中，可能还有 await ）可能会被您的处理人员清除，这肯定会让您头疼。

There are many other control exceptions, and so it is wise to only match on CX::Warn rather than use default. Otherwise, take, next, last, emit, done (and, in 6.d, probably also await) could be netted by your handler, which would surely make for quite some headaches.

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