perl - Perl 中的 Given-when-continue 语句

Question

我是从 www.perltutorial.org 学习 Perl 的.在那里我了解到 given-when 就像 switch-case。因此为了练习我写了下面的脚本。现在我开始知道 break 是 given-when 中固有的，为了成功，我需要使用 continue 语句。

当我给出“甜蜜”的输入时，它给出的输出是“像真人一样”。不应该输出为

"Honey just put your sweet lips on my lips\n
We should just kiss like real people do" 

代码如下:

#!/usr/bin/perl
use strict;
use warnings;
use feature "switch";
my $choice = <STDIN>;
my $msg ="";
chomp($choice);
given(lc $choice){
    when('a'){
        $msg = "I had a thought, dear";
    }
    when('b'){
        $msg = "However scary";
    }
    when('c'){
        $msg = "About that night";
    }
    when('d'){
        $msg = "The bugs and the dirt";
    }
    when('e'){
        $msg = "Why were you digging?";
    }
    when('sweet'){
        $msg =  "Honey just put your sweet lips on my lips ";
        continue;
    }
    when('lips'){
        $msg = $msg."\nWe should just kiss like real people do";
    }
    default{
        $msg = "";
    }
}

#print($msg,"\n");
unless($msg eq "") {
    print($msg, "\n");
}else{
    print("Like real People do!\n");
}

Answer 1

[请注意，智能匹配功能是实验性的，它被认为设计有缺陷。通过扩展，开关功能也是如此，因为它使用智能匹配。这些应该避免。]

实际上，$msg 包含空字符串。

#!/usr/bin/perl
use strict;
use warnings;
use feature qw( say switch );
my $choice = "sweet\n";
chomp($choice);
my $msg ="";
given(lc $choice){
    # ...
    when('e'){
        $msg = "Why were you digging?";
    }
    when('sweet'){
        $msg = "Honey just put your sweet lips on my lips\n";
        continue;
    }
    when('lips'){
        $msg .= "We should just kiss like real people do";
    }
    default{
        $msg = "";
    }
}

say ">$msg<";

输出:

given is experimental at a.pl line 8.
when is experimental at a.pl line 10.
when is experimental at a.pl line 14.
when is experimental at a.pl line 17.
><

continue 导致执行继续到 when 语句之后的语句。下一个语句是 when('lips'){ ... }，它什么都不做(因为 "sweet"~~ "lips" 是 false)。之后的语句是 default { $msg = ""; } 清除 $msg，因为自从我们继续以来没有执行 when。

要获得所需的结果，您需要具备以下条件:

given(lc $choice){
    # ...
    when('e'){
        $msg = "Why were you digging?";
    }
    when('sweet'){
        $msg = "Honey just put your sweet lips on my lips\n";
        continue;
    }
    when($_ ~~ 'sweet' || $_ ~~ 'lips'){
        $msg .= "We should just kiss like real people do";
    }
    default{
        $msg = "";
    }
}

如果没有实验性的开关和智能匹配功能，我们可以使用

for (lc $choice) {
    # ...
    if ($_ eq 'e'){
        $msg = "Why were you digging?";
        last;
    }
    if ($_ eq 'sweet'){
        $msg = "Honey just put your sweet lips on my lips\n";
        last;
    }
    if ($_ eq 'sweet' || $_ eq 'lips'){
        $msg .= "We should just kiss like real people do";
        last;
    }
    $msg = "";
}

或

for (lc $choice) {
    # ...
    if ($_ eq 'e'){
        $msg = "Why were you digging?";
    }
    elsif ($_ eq 'sweet' || $_ eq 'lips'){
        if ($_ eq 'sweet'){
            $msg = "Honey just put your sweet lips on my lips\n";
        }

        $msg .= "We should just kiss like real people do";
    }
    else {
        $msg = "";
    }
}