对哈希kv对进行排序

由于在列表上调用.kv会返回一个您不想要的索引列表,即Pair列表;你不能只调用.kv.所以你必须通过在每个对象上调用.kv方法单独从列表中的Pair对象中取出键和值,其中>> .kv.

您也可以使用.map(*.kv)代替.

>> .kv语法允许实现在多个线程上传播工作,如果这样做有意义的话.
(目前Rakudo只是以半随机顺序完成工作,以防止人们使用该功能错误)

通过使用子签名中的副词提取属性,可以使用另一种方法编写循环：

for %hash.sort -> (:$key,:$value) {
  say "'$key' => '$value'";
}

for %hash.sort -> $pair (:$key,:$value) {
  say $pair;
  say $key === $pair.key and $value === $pair.value; # True?
}

# :$key is short for :key($key)
for %hash.sort -> (:key($k),:value($v)) {
  say "'$k' => '$v'";
}

这对于没有创建公共属性列表的方法的其他对象非常有用

class C { has $.a; has $.b; has $.c; has $!private-value }
my $c = 5;
my $obj = C.new(:a<A>,:b(1),:$c);

given $obj -> ( :$a,:b($b),:$c) ) {
  say "$a $b $c";
}

# ignore $.a by using an unnamed scalar
given $obj -> ( :a($),:$b,:$c ) { ... }

# places any unspecified public attributes in %others
given $obj -> ( :$a,*%others ) {
  .say for keys %others; # c?
}

# ignores any unspecified attributes
# useful to allow subclasses to add more attributes
# or to just drop any values you don't care about
given $obj -> ( :$a,*% ) { ... }

# fails because it doesn't handle the public c attribute
# in the sub-signature
given $obj -> ( :$a,:$b ) { ... }

这只是签名可能的开始.

在子例程和方法签名中也允许以下所有内容,可选,并且对于此示例完全过度杀伤.
它在用于限制可能的候选者的多子方法和多方法中非常有用.

for 'one' => 1,1/3
->
  # Type is an alias to the object type
  ::Type Any $_ # Any is the default type requirement

  # the public attributes of the object
  (
    ::A-Type Any :key(   :numerator(   $a ) ),::B-Type Any :value( :denominator( $b ) ) where $b >= 1,)
{
  my Type $obj = $_; # new variable declared as having the same type
  my A-Type $new-a = $a;
  my B-Type $new-b = $b;

  # could have used $_.^name or .^name instead of Type.^name
  # so you don't actually have to add the alias to the signature
  # to get the name of the arguments type
  say Type.^name,' ',$_;
  say '  ',A-Type.^name,$a;
  say '  ',B-Type.^name,$b;
}

Pair one => 1
  Str one
  Int 1
Rat 0.333333
  Int 1
  Int 3

至于使用.sort({.key}),是的,这基本上是一回事,因为sort接受任何Callable.

我想指出你甚至不需要为sort提供一个参数,因为它的默认值甚至比你给它的更聪明.

Perl 6有很多方法可以创建和访问Callable.所以以下任何一个都有效：

*.key
{ .key } # { $_.key }
-> $_ { .key } # basically what the previous line turns into
{ $^placeholder-var.key }
sub ($_) { .key }
&a-subroutine-reference # you would have to create the subroutine though

此外,因为所有普通操作符实际上都是子例程,所以你可以在需要Callable的其他地方使用它们.(我想不出那个在那个地方工作的那个)

&infix:<+> # the subroutines responsible for the numeric addition operator
&[+] # ditto

&prefix:<++>
&postfix:<++>

# etc