Perl, need advice - what does the above code do?

Question

Perl

There is a code that compares two arrays and puts elements from the @spisok2 array that are not found in the @spisok1 array into the @diff array:

#! /usr/bin/perl
@spisok1=(1,2,3,4,5,6);
@spisok2=(1,2,3,4,5,7,8);
@diff=();
%seen = ();
@seen{@spisok1} = ();
foreach $item(@spisok2)
       {
         push(@diff, $item) unless exists $seen{$item};
        }
printf ("@diff\n");

Outputs as it should:
>7 8
The code was taken from somewhere on the Internet and used 'as is''.
Now there is a need to figure it out, and I found that I don’t understand this construction:
@seen{@spisok1} = ();
Tell me, plz, what is it and how does it work. Well, or where to read about it, because nothing intelligible was found by Google.
Thank you.

Answer 1

This line fills in a hash called %seen.
The elements of the @spisok1 array are substituted as the keys of this hash, and the values ​​are empty.
And if we replace this line with a loop, we get:

for my $element (@spisok1) { 
    $seen{$element} = undef;
}

This entry will be equivalent to your string.

Answer 2

I will add that such a construction is called a "slice" of the hash. Slicing can also be applied to arrays (lists).
Pay attention to the sigil - when working with a slice, it points to an array - @