我如何在Perl中创建一个新的空哈希引用？ [英] How can I make a new, empty hash reference in Perl?

问题描述

假设我有类似的东西：

 ＃％superhash是一些具有多于0个键的预定义散列; 
％hash =（）; 
 foreach我的$ key（键值％superhash）{
 $ superhash {$ key} =％hash; 
％hash =（）; 
 
 $ / code> 

superhash的所有键都指向与％hash 或者它们会是不同的空哈希？

如果不是，我怎么确定它们指向空哈希？ 复制到复数数据类型（数组或散列），然后才能将其存储到其中一个单独的插槽中。但是在给出的示例代码中，如果引用它们，每个代码都是相同的散列。

初始化数据结构的方式是：

  foreach my $ key（keys％superhash）{
 $ superhash {$ key} = {}; ＃新的空散列引用
} 
  

但是，像这样的初始化在 Perl 由于autovivification（当变量用作容器时创建适当的容器对象）。

  my％hash; 
 
 $ hash {a} {b} = 1; 
  

现在％hash 有一个键，'' a'，其具有匿名hashref的值，其包含键/值对 b => 1 。数组以相同的方式自动生成。

Say I had something like:

# %superhash is some predefined hash with more than 0 keys;
%hash = ();
foreach my $key (keys %superhash){
    $superhash{ $key } = %hash;
    %hash = ();
}

Would all the keys of superhash point to the same empty hash accessed by %hash or would they be different empty hashes?

If not, how can I make sure they point to empty hashes?

解决方案

You need to use the \ operator to take a reference to a plural data type (array or hash) before you can store it into a single slot of either. But in the example code given, if referenced, each would be the same hash.

The way to initialize your data structure is:

foreach my $key (keys %superhash) {
    $superhash{ $key } = {}; # New empty hash reference
}

But initialization like this is largely unnecessary in Perl due to autovivification (creating appropriate container objects when a variable is used as a container).

my %hash;

$hash{a}{b} = 1;

Now %hash has one key, 'a', which has a value of an anonymous hashref, containing the key/value pair b => 1. Arrays autovivify in the same manner.

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