问题

Here's the translated content you requested:

我发现了这个JS代码片段：
```js
function append(demo = "", file = "") {
    const extra = "ctl=1&embed=1";
    if (demo && file)  return `/${demo}/?file=${file}&${extra}`;
    if (!demo && file) return `/?file=${file}&${extra}`;
    if (demo && !file) return `/${demo}&${extra}`;
    return `?${extra}`; 
}

我可以轻松地将这个代码移植到Raku，并使用if语句，但我认为使用given/when语句来展示这个特性会是一种不错的方式。我想出了以下代码：

sub append(Str :$demo, Str :$file) {
    my $extra = "ctl=1&embed=1";
    given ($demo, $file) {
        when $demo.so,  $file.so  { "/$demo/?file=$file&$extra" } 
        when $demo.not, $file.so  { "/?file=$file&$extra" } 
        when $demo.so,  $file.not { "/$demo?$extra" } 
        default                   { "?$extra" }
    }
}

say append :file("here"), :demo("there"); # /there/?file=here&ctl=1&embed=1
say append :file("here");                 # /?file=here&ctl=1&embed=1
say append :demo("here");                 # /here?ctl=1&embed=1
say append;                               # ?ctl=1&embed=1

然而，这段代码相当重复，而且我甚至不确定它是否符合Raku的习惯用法，所以我想我可以这样做：

sub append(Str :$demo = '', Str :$file = '') {
    my $extra = "ctl=1&embed=1";
    given ($demo.so, $file.so) {
        when (True,  True)  { "/$demo/?file=$file&$extra" } 
        when (False, True)  { "/?file=$file&$extra" } 
        when (True,  False) { "/$demo?$extra" } 
        default             { "?$extra" }
    }
}

然而，这并不能按预期工作。因此，是否有可能将一系列值绑定到主题变量$_，然后使用when语句进行智能匹配？我（误）记得Daniel“codesections”Sockwell曾经做过类似的事情，但我记不清在哪里看到的了。

Please note that I've retained the HTML entity references (e.g., `"`) in the translated content as they were in the original text. If you have any specific questions or requests related to this code or translation, feel free to ask.

<details>
<summary>英文:</summary>

I came across this JS code snippet:
```js
function append(demo = &quot;&quot;, file = &quot;&quot;) {
    const extra = &quot;ctl=1&amp;embed=1&quot;;
    if (demo &amp;&amp; file)  return `/${demo}/?file=${file}&amp;${extra}`;
    if (!demo &amp;&amp; file) return `/?file=${file}&amp;${extra}`;
    if (demo &amp;&amp; !file) return `/${demo}&amp;${extra}`;
    return `?${extra}`; 
}

I can port this easily to Raku using ifs but I thought using given/when would be a nice way of showcasing that feature. I came up with the following:

sub append(Str :$demo, Str :$file) {
    my $extra = "ctl=1&embed=1";
    given ($demo, $file) {
        when $demo.so,  $file.so  { "/$demo/?file=$file&$extra" } 
        when $demo.not, $file.so  { "/?file=$file&$extra" } 
        when $demo.so,  $file.not { "/$demo?$extra" } 
        default                   { "?$extra" }
    }
}

say append :file("here"), :demo("there"); # /there/?file=here&ctl=1&embed=1
say append :file("here");                 # /?file=here&ctl=1&embed=1
say append :demo("here");                 # /here?ctl=1&embed=1
say append;                               # ?ctl=1&embed=1

However it's quite repetitive and I'm not even sure if it's idiomatic Raku so I figured I could do the following:

sub append(Str :$demo = '', Str :$file = '') {
    my $extra = "ctl=1&embed=1";
    given ($demo.so, $file.so) {
        when (True,  True)  { "/$demo/?file=$file&$extra" } 
        when (False, True)  { "/?file=$file&$extra" } 
        when (True,  False) { "/$demo?$extra" } 
        default             { "?$extra" }
    }
}

This doesn't work as expected though. Thus, is it even possible to bind a list of values to the topic variable $_ and smartmatch against it with whens? I (mis)remember Daniel "codesections" Sockwell doing something to this extent but I cannot remember where.

答案1

得分: 4

我运行了你的代码并得到了这个错误：

在字符串上下文中使用了未初始化的 Str 类型值。
可以使用 .^name、.raku、.gist 或 .say 方法将其转换为有意义的内容。

你可以在 append() 签名中添加默认值来初始化参数值，就像这样：

sub append(Str :$demo='', Str :$file='') {

而且不需要使用 do given，普通的 given 就可以。

Use of uninitialized value of type Str in string context.
Methods .^name, .raku, .gist, or .say can be used to stringify it to something meaningful.

sub append(Str :$demo='', Str :$file='') {

答案2

得分: 2

> 我提出了以下

这是巧合的。您对True使用smartmatch

在这种情况下，您不需要给出:

sub append(Str :$demo, Str :$file, :$extra = "ctl=1&embed=1") {
    when $demo.so  &  $file.so  { "/$demo/?file=$file&$extra" }
    when              $file.so  { "/?file=$file&$extra" }
    when $demo.so               { "/$demo?$extra" }
    default                     { "?$extra" }
}

> 我可以将值列表绑定到主题变量$_并使用whens进行智能匹配吗?

可以的:

sub append(Str :$demo, Str :$file, :$extra = "ctl=1&embed=1") {
    given ($demo, $file) {
        when :so , :so  { "/$demo/?file=$file&$extra" }
        when :!so, :so  { "/?file=$file&$extra" }
        when :so , :!so { "/$demo?$extra" }
        default         { "?$extra" }
    }
}

您可以对Signature使用smartmatch:

sub append(|c (Str :$demo, Str :$file)) {
    my $extra = "ctl=1&embed=1";
    given c {
        when :(:demo($)!, :file($)!)  { "/$demo/?file=$file&$extra" }
        when :(:file($)!)             { "/?file=$file&$extra" }
        when :(:demo($)!)             { "/$demo?$extra" }
        default                       { "?$extra" }
    }
}

但使用multi-dispatch更有趣:

constant $extra = 'ctl=1&embed=1';
proto append (Str :$demo,Str :$file) {*}
multi append (:$demo!, :$file!) { "/$demo/?file=$file&$extra" }
multi append (:$file!)          { "/?file=$file&$extra" }
multi append (:$demo!)          { "/$demo?$extra" }
multi append ()                 { "?$extra" }

sub append(Str :$demo, Str :$file, :$extra = "ctl=1&embed=1") {
    when $demo.so  &  $file.so  { "/$demo/?file=$file&$extra" }
    when              $file.so  { "/?file=$file&$extra" }
    when $demo.so               { "/$demo?$extra" }
    default                     { "?$extra" }
}

sub append(Str :$demo, Str :$file, :$extra = "ctl=1&embed=1") {
    given ($demo, $file) {
        when :so , :so  { "/$demo/?file=$file&$extra" }
        when :!so, :so  { "/?file=$file&$extra" }
        when :so , :!so { "/$demo?$extra" }
        default         { "?$extra" }
    }
}

sub append(|c (Str :$demo, Str :$file)) {
    my $extra = "ctl=1&embed=1";
    given c {
        when :(:demo($)!, :file($)!)  { "/$demo/?file=$file&$extra" }
        when :(:file($)!)             { "/?file=$file&$extra" }
        when :(:demo($)!)             { "/$demo?$extra" }
        default                       { "?$extra" }
    }
}

constant $extra = 'ctl=1&embed=1';
proto append (Str :$demo,Str :$file) {*}
multi append (:$demo!, :$file!) { "/$demo/?file=$file&$extra" }
multi append (:$file!)          { "/?file=$file&$extra" }
multi append (:$demo!)          { "/$demo?$extra" }
multi append ()                 { "?$extra" }