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Mimosinnet
Asked: 2024-01-07 11:23:07 +0800 CST

是否可以在映射块中使用数组的索引？

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我想在映射例程中使用数组的索引。例如，这个 Raku 代码：

raku -e 'my @a = "First", "Second", "Third", "First"; say @a.map({ "Index of $_ is: ;" })'

印刷：

(Index of First is: ; Index of Second is: ; Index of Third is: ; Index of First is: ;)

是否可以获取数组的索引，例如：

(Index of First is: 0; Index of Second is: 1; Index of Third is: 2; Index of First is: 3;)

谢谢！

dictionary

1 个回答

  1. Best Answer

    需要.kv产生“键”和值。对于数组，键是索引 0、1、2...

     >>> my @a = "First", "Second", "Third", "First";
[First Second Third First]

>>> @a.kv
(0 First 1 Second 2 Third 3 First)

    这是一个长度为 2N 的平坦序列；我们可以map通过显式签名一次获取两件事：

    >>> @a.kv.map(-> $index, $value { "Index of $value is $index;" })
(Index of First is 0; Index of Second is 1; Index of Third is 2; Index of First is 3;)

    或通过占位符变量：

    >>> @a.kv.map({ "Index of $^value is $^index;" })
(Index of First is 0; Index of Second is 1; Index of Third is 2; Index of First is 3;)

    由于索引按字典顺序出现在值之前，因此其工作方式与前面的显式签名情况相同，即在幕后为我们生成相同的签名。我们可以看到这个：

    >>> &{ $^value, $^index }
-> $index, $value { #`(Block|140736965530488) ... }

    请注意，重要的是变量名称的 Unicode 顺序，而不是出现的顺序。

    本着 TIMTOWDI 的精神，一些替代方案（IMO 不是更好）：

    # Limitation: generated anew per closure and per mention,
# so cannot use, e.g., in string interpolations with closure and more than once
>>> @a.map({ "Index of $_ is " ~ $++ ~ ";" })
(Index of First is 0; Index of Second is 1; Index of Third is 2; Index of First is 3;)
    • 使用.pairs, tableine of.kv生成“key => value”对而不是平面列表
    >>> @a.pairs
(0 => First 1 => Second 2 => Third 3 => First)

# Reach over .key & .value
>>> @a.pairs.map({ "Index of $_.value() is $_.key();" })
(Index of First is 0; Index of Second is 1; Index of Third is 2; Index of First is 3;)

# Unpack with signature
>>> @a.pairs.map(-> (:key($index), :$value) { "Index of $value is $index;" })
(Index of First is 0; Index of Second is 1; Index of Third is 2; Index of First is 3;)
    • 我们可以映射数组的键，而不是映射数组的值本身：
    # Array.keys produces 0, 1, 2...
>>> @a.keys.map({ "Index of @a[$_] is $_;" })
(Index of First is 0; Index of Second is 1; Index of Third is 2; Index of First is 3;)

# ^@a is equivalent to ^@a.elems === 0 ..^ @a.elems, i.e., 0, 1, 2... again
>>> ^@a .map({ "Index of @a[$_] is $_;" })
(Index of First is 0; Index of Second is 1; Index of Third is 2; Index of First is 3;)

    我认为最后一个是最不惯用的。

    • 11

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