我应该如何处理行（）无法读取的Perl 6 $ * ARGFILES？ [英] How should I handle Perl 6 $*ARGFILES that can't be read by lines()?

问题描述

我正在玩行，它会从您在命令行中指定的文件中读取行：

I'm playing around with lines which reads lines from the files you specify on the command line:

for lines() { put $_ }

如果是无法读取它抛出的其中一个文件名 X :: AdHoc （有一天它可能有更好的异常类型，所以我们可以用 .path 方法）。很好，所以赶上：

If it can't read one of the filenames it throws X::AdHoc (one day maybe it will have better exception types so we can grab the filename with a .path method). Fine, so catch that:

try {
CATCH { default { put .^name } }
for lines() { put $_ }
}

所以这就抓住了 X :: AdHoc 错误，但就是这样。此时尝试块已完成。它不能 .resume 并尝试下一个文件：

So this catches the X::AdHoc error but that's it. The try block is done at that point. It can't .resume and try the next file:

try {
CATCH { default { put .^name; .resume } }  # Nope
for lines() { put $_ }
}

回到Perl 5的土地，你会收到关于文件名错误的警告，然后程序转到下一个文件。

Back in Perl 5 land you get a warning about the bad filename and the program moves on to the next thing.

我可以过滤 @ * ARGS 首先重建 $ * ARGFILES 如果有一些参数：

I could filter @*ARGS first then reconstruct $*ARGFILES if there are some arguments:

$*ARGFILES = IO::CatHandle.new:  
    @*ARGS.grep( { $^a.IO.e and $^a.IO.r } ) if +@*ARGS;

for lines() { put $_ }

虽然有效默默地忽略坏文件。我可以处理这个但是我自己处理参数列表有点乏味，包括 - 标准输入作为文件名，默认情况下没有参数：

That works although it silently ignores bad files. I could handle that but it's a bit tedious to handle the argument list myself, including - for standard input as a filename and the default with no arguments:

my $code := { put $_ };

@*ARGS = '-' unless +@*ARGS;
for @*ARGS -> $arg {
    given $arg {
        when '-'     { $code.($_) for $*IN.lines(); next }
        when ! .IO.e { note "$_ does not exist";    next }
        when ! .IO.r { note "$_ is not readable";   next }
        default      { $code.($_) for $arg.IO.lines() }
        }
    }

但这是很多工作。有没有更简单的方法来处理这个？

But that's a lot of work. Is there a simpler way to handle this?

推荐答案

要警告糟糕的打开并继续前进，你可以使用这样的东西：

To warn on bad open and move on, you could use something like this:

$*ARGFILES does role { method next-handle { loop {
    try return self.IO::CatHandle::next-handle;
    warn "WARNING: $!.message"
}}}

.say for lines

只需混合角色即可使 IO :: CatHandle.next-handle 方法重试下一个句柄。 （您也可以使用 但运营商来反而在混合中使用）。

Simply mixing in a role that makes the IO::CatHandle.next-handle method re-try getting next handle. (you can also use but operator to mixin on a copy instead).

如果它无法读取其中一个文件名抛出X :: AdHoc

If it can't read one of the filenames it throws X::AdHoc

X :: AdHoc 来自 .open call;有一个有点发霉的PR可以输入这些例外，所以一旦修复， IO :: CatHandle 也会抛出类型异常。

The X::AdHoc is from .open call; there's a somewhat moldy PR to make those exceptions typed, so once that's fixed, IO::CatHandle would throw typed exceptions as well.

它不能.resume

It can't .resume

是的，你只能从捕获它的 CATCH 块中恢复，但是在这种情况下，它被捕获到 .open 调用并被转换为失败，然后由<$ c接收$ c> IO :: CatHandle.next-handle 及其 .exception 重新< - code> .throw n。

Yeah, you can only resume from a CATCH block that caught it, but in this case it's caught inside .open call and is made into a Failure, which is then received by IO::CatHandle.next-handle and its .exception is re-.thrown.

然而，即使它在这里可以恢复，它也会简单地恢复到抛出异常的路径，而不是用另一个句柄重新尝试。这没有用。 （我调查了它可以恢复，但这增加了 on-switch 的模糊性，我不习惯指出恢复异常来自某些地方必须能够有意义地继续 - 我们目前不为核心地点提供这样的保证。）

However, even if it were resumable here, it'd simply resume into a path where exception was thrown, not re-try with another handle. It wouldn't help. (I looked into making it resumable, but that adds vagueness to on-switch and I'm not comfortable speccing that resuming Exceptions from certain places must be able to meaningfully continue—we currently don't offer such a guarantee for any place in core).

包括 - 标准输入作为文件名

请注意那个特殊含义是离开在6.d语言至 IO :: Handle.open （以及扩展名 IO :: CatHandle.new ）去了。它可能会在 IO :: ArgFiles 中得到特殊处理，但我没有看到提议。

Note that that special meaning is going away in 6.d language as far as IO::Handle.open (and by extension IO::CatHandle.new) goes. It might get special treatment in IO::ArgFiles, but I've not seen that proposed.

回到Perl 5之后，你会收到关于文件名错误的警告，然后程序转到下一步。

Back in Perl 5 land you get a warning about the bad filename and the program moves on to the next thing.

在Perl 6中，它实现为通用的 IO :: CatHandle 类型，用户可以用于任何事情，而不仅仅是文件参数，默认情况下警告和继续对我来说太麻烦了。

In Perl 6, it's implemented as a generalized IO::CatHandle type users can use for anything, not just file arguments, so warning and moving on by default feels too lax to me.

IO :: ArgFiles 可能是特殊的提供这样的行为。就个人而言，我反对整个地方的特殊外壳，我认为这是Perl 5中最大的缺陷，但你可以打开一个提议的问题并查看是否有人支持它。

IO::ArgFiles could be special-cased to offer such behaviour. Personally, I'm against special casing stuff all over the place and I think that is the biggest flaw in Perl 5, but you could open an Issue proposing that and see if anyone backs it.

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