如何在子例程中取消引用散列并像在调用例程中一样对其进行处理？

Question

我有一个 perl 例程，它从 .csv 文件中生成散列。应在子例程中检查这些值。

所以我有一个散列 %my_values 并调用子例程 check (\%my_values):

sub read_csv {
    ...

    # key:   headline entry
    # value: the value in the current row
    %my_hash;

    ...
    my ($has_error, $err_msg) = check (\%my_hash);
}

sub check {
    my($hash_ref) = @_;
    %my_hash = %$hash_ref;

    # Get the artikel number of the article
    $my_hash {'article_number'} = get_artnr($my_hash {'article'});
    if (not $my_hash{'article_number'}) {
        return 1, "Article $my_hash{'article'} not found!";
    }

    # check price (I'm in germany, there must be a conversation from ',' to '.')
    $my_hash {'price'} =~ s/,/./;
    if (not $my_hash{'price'} =~ m/^\d+(\.\d+)?$/) {
        return 1, "Invalid format of price";
    }

    return 0, "";
}

起初，这似乎工作正常。但后来我意识到，价格格式既没有改变，也没有密钥 article_number 可用。

直接在参考上工作使其成为：


# In this case, it works!
sub check {
    my($hash_ref) = @_;

    # Get the artikel number of the article
    $hash_ref->{'article_number'} = get_artnr($hash_ref->{'article'});
    if (not $hash_ref->{'article_number'}) {
        return 1, "Article $hash_ref->{'article'} not found!";
    }

    # check price (I'm in germany, there must be a conversation from ',' to '.')
    $hash_ref->{'price'} =~ s/,/./;
    if (not $hash_ref->{'price'} =~ m/^\d+(\.\d+)?$/) {
        return 1, "Invalid format of price";
    }

    return 0, "";
}

所以我认为 %my_hash = %$hash_ref; 复制引用而不是取消引用。

如何在子例程中取消引用散列并像在调用例程中一样对其进行处理？

Answer 1

这是一个使用 5.26 中引入的名为 refaliasing introduced in Perl 5.22 (optionally combined with the declared_refs 的新功能的示例)

use v5.26;
use warnings;  # IMPORTANT: this line must come before "use experimental"
use strict;
use feature qw(say); 
use experimental qw(declared_refs refaliasing);

{  # <-- introduce scope to avoid leaking lexical variables into subs below
    my %hash = (a=>1, b=>2);
    check(\%hash);
    say "Value of 'a' key is now: ", $hash{a};
}

sub check {
    my (\%hash) = @_;

    $hash{a} = 3;
}

输出:

Value of 'a' key is now: 3

或者您可以使用 arrow operator:

sub check {
    my ($hash) = @_;

    $hash->{a} = 3;
}

如何在子例程中取消引用散列并像在调用例程中一样对其进行处理？

How can I dereference a hash in a subroutine an work on it like in the calling routine?

perl

hash

reference

subroutine