perl中这个变量的数据结构是什么？

发布于 2024-12-20 06:29:20 字数 207 浏览 2 评论 0原文

我是 Perl 新手，正在阅读用 Perl 编写的代码。一行内容如下：

$Map{$a}->{$b} = $c{$d};

我熟悉哈希看起来像 %samplehash 并通过 $samplehash{a}="b" 访问，

但是上面的行说明了什么实际上是地图吗？

原文

I am new to perl and reading a code written in perl. A line reads like this:

$Map{$a}->{$b} = $c{$d};

I am familiar with hash looking like %samplehash and accessed as $samplehash{a}="b"

but what does the above line say about what is Map actually?

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万劫不复 2024-12-27 06:29:20

给定这些变量：

my $a = "apples";
my $b = "pears";
my %c = ("bananas" => 2);
my $d = "bananas";
my %Map;

赋值

$Map{$a}->{$b} = $c{$d};

结果看起来像这样的哈希：

%Map = (
    "apples" => {
        "pears" => 2
    }
);

%Map 是一个哈希，在赋值之后通过自动激活包含哈希引用：如果尚不存在，则自动创建内部哈希引用通过 Perl 通过访问 %Map 哈希中的元素 $Map{$a}->{$b} 来实现。

Given these variables:

my $a = "apples";
my $b = "pears";
my %c = ("bananas" => 2);
my $d = "bananas";
my %Map;

The assignment

$Map{$a}->{$b} = $c{$d};

Results in a hash looking like this:

%Map = (
    "apples" => {
        "pears" => 2
    }
);

%Map is a hash, which after the assignment contains a hash ref through autovivification: If not already there, the inner hash ref is automatically created by Perl by accessing the element $Map{$a}->{$b} in the %Map hash.

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万劫不复 2024-12-27 06:29:20

$Map{$a}->{$b}

相当于

${ $Map{$a} }{$b}

只

$hash{$b}

使用哈希引用 $Map{$a} 而不是 %hash。

请参阅 http://perlmonks.org/?node=References+quick+reference关于如何使用嵌套数据结构的一些容易记住的规则。

此外，在自动激活（默认情况下）的情况下，如果 $Map{$a} 以不存在或 undef 的形式启动，它将被隐式初始化为新的哈希引用。

$Map{$a}->{$b}

is equivalent to

${ $Map{$a} }{$b}

which is like

$hash{$b}

only using the hash reference $Map{$a} instead of %hash.

See http://perlmonks.org/?node=References+quick+reference for some easy to remember rules about how to use nested data structures.

Additionally, with autovivification on (which it is by default), if $Map{$a} starts as not existing or undef, it will be implicitly initialized to be a new hash reference.

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