Re: Syntax explanation required

[eyepopslikeamosquito]

Two alternative ways derived from: perldoc -q duplicate

my %seen;
my @uniq = grep { !$seen{$_}++ } keys(%hash1), keys(%hash2);

use List::MoreUtils qw(uniq);
my @uniq = uniq( keys(%hash1), keys(%hash2) );

[LanX]

I was meditating about advising List::MoreUtils:uniq as a best practice, cause I thought it prevents any stringification problems.¹

Unfortunately it doesn't! :(

  DB<125> $a=["A"]
 => ["A"]
 
  DB<126> $b=["B"]
 => ["B"]
 
  DB<127> @a=($a,"$a",$b,"$b")
 => (["A"], "ARRAY(0x96cb0f0)", ["B"], "ARRAY(0x96cfd80)")
 
  DB<128> @b= uniq @a
 => (["A"], ["B"])

thats quite disappointing for an XS-module ...

EDIT: Well at least it preserves order...

¹) I should explain, the problem with using hashes for set operations is that keys are stringified, that means working with anything which isn't a string or at least a scalar comes with a risk.

Practically it's not possible to safely use a ref as a key because of the resulting string is irreversible.

  DB<130> $h{$a}=5
 => 5
 
  DB<131> %h
 => ("ARRAY(0x96d1f00)", 5)

UPDATE:

improved code example...

[ghosh123]

Thank you all. Very helpful !!!