Perl中提供了哪种语法糖来减少l/rvalue运算符与if语句的代码? [英] What kind of syntactic sugar is available in Perl to reduce code for l/rvalue operators vs. if statements?

问题描述

那里有很多，因为Perl是一种非常含糖的语言，但是任何一种语言中最常用的语句是if语句和设置值的组合.我想我找到了很多，但是仍然有一些差距.最终，目标是不必多次写一个变量名:

There's a bunch out there, as Perl is a pretty sugary language, but the most used statements in any language is the combination of if statements and setting values. I think I've found many of them, but there's still a few gaps. Ultimately, the goal would be to not have to write a variable name more than once:

这是我到目前为止所拥有的:

Here's what I have so far:

$r ||= $s;          # $r = $s unless ($r);
$r //= $s;          # $r = $s unless (defined $r);
$r &&= $s;          # $r = $s if ($r);
$r = $c ? $s : $t;  # if ($c) { $r = $s } else { $r = $t }
$c ? $r : $s = $t;  # if ($c) { $r = $t } else { $s = $t }
$r = $s || $t;      # if ($s) { $r = $s } else { $r = $t }
$r = $s && $t;      # if ($s) { $r = $t } else { $r = $s = undef, 0, untrue, etc. }
$c and return $r;   # return $r if ($c);
$c or  return $r;   # return $r unless ($c);
$c and $r = $s;     # $r = $s if ($c);
@$r{qw(a b c d)}    # ($r->{a}, $r->{b}, $r->{c}, $r->{d})

某人在秘密操作员"上还有一条真正有趣的文章，如下所示:

Somebody also had a really interesting article on a "secret operator", shown here:

my @part = (
    'http://example.net/app',
    ( 'admin'  ) x!! $is_admin_link,
    ( $subsite ) x!! defined $subsite,
    $mode,
    ( $id      ) x!! defined $id,
    ( $submode ) x!! defined $submode,
);

但是，我发现列表中缺少的是:

However, what I've found to be missing from the list is:

$r <= $s;                 # read as "$r = min($r, $s);" except with short-circuiting
$r = $s if (defined $s);  # what's the opposite of //?
$r and return $r          # can that be done without repeating $r?

还有其他值得补充的地方吗?还有哪些其他条件设置变量可用于减少代码?还缺少什么?

Is there anything else worth adding? What other conditional set variables are available to reduce the code? What else is missing?

推荐答案

使用低优先级的and和or关键字，可以更清楚地编写您问题中的这些结构:

These structures from your question could be written a little bit more clearly using the low precedence and and or keywords:

$c and return $r;    # return $r if ($c);
$c or return $r;     # return $r unless ($c);
$c and $r = $s;      # $r = $s if ($c);

and和or的好处是，与语句修饰符控制字不同，and和or可以链接到复合表达式中.

The nice thing about and and or is that unlike the statement modifier control words, and and or can be chained into compound expressions.

另一个用于语法糖的有用工具是将for/foreach循环用作单个值的主题划分器.请考虑以下内容:

Another useful tool for syntactic sugar is using the for/foreach loop as a topicalizer over a single value. Consider the following:

$var = $new_value if defined $new_value;

vs

defined and $var = $_ for $new_value;

或类似的东西

$foo = "[$foo]";
$bar = "[$bar]";

$_ = "[$_]" for $foo, $bar;

map函数也可以以这种方式使用，并且具有可以使用的返回值.

the map function can also be used in this manner, and has a return value you can use.

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