展平Perl哈希数组

Question

Currently have this demonstration code:

use 5.012;
use Data::Dump;

my $AoH = [
    {a => "aval"},  #exactly only one key-value
    {b => "bval"},  #for each
    {c => "cval"},  #array element
];

dd $AoH;

my @arr = map { each $_ } @$AoH;
dd @arr;

it works and produces my wanted result

[{ a => "aval" }, { b => "bval" }, { c => "cval" }]
("a", "aval", "b", "bval", "c", "cval")

The question is: is correct the the map { each $_ } construction, or it is possible to do it with "another way"?

Answer 1

Just dereference the hashrefs:

my $AoH = [
    {a => "aval"},  #exactly only one key-value
    {b => "bval"},  #for each
    {c => "cval"},  #array element
];

# Flatten the hash refs
my @arr = map { %$_ } @$AoH;

I'd advise against using each in that context. From perldoc :

Starting with Perl 5.14, each can take a scalar EXPR , which must hold reference to an unblessed hash or array. The argument will be dereferenced automatically. This aspect of each is considered highly experimental. The exact behaviour may change in a future version of Perl.

Answer 2

is correct the the map { each $_ } construction,

Not exactly. In your specific case, it will do what you want. However, as pointed out by @ikegami, this will introduce a subtle bug in your code, do what you did twice, you will see the problem. Every hash has a internal iterator, and this iterator will be reset only after you exhausted that hash, and read it once more. (It is similar to feof() .)

Additionally, each $_ only available since Perl 5.14 or later, for early versions, you need to use map { each %$_ } .

However, the REAL problem is that there is no need to use each , you could use map { %$_ } , in list context, hash will return a list made up of its key-value pairs.

or it is possible to do it with "another way"?

Also yes, you could use foreach and push , like this:

push @arr, %$_ foreach @$AoH;

However, this is basically the same as your method.