It's really no different than a shift.

If I understand perlsub, the subtlety here is that @_ itself is not an alias to the original array/list of arguments -- rather, @_ is a local array with each element an alias to the corresponding element in the argument list -- which is why you can shift, pop or (as in this case) splice @_ at will.

However, assigning to @_ or even using splice to overwrite part of an array, destroys that aliasing for whatever is overwritten. Thus:

use strict;
use warnings;

sub splice_insert {
    splice( @_, 2, 2, ('a' .. 'c') );
    print "@_ # after splice\n";
    $_ = '.' for @_;
    print "@_ # after for loop\n";
}

my @a = ( 0 .. 6 );

print "@a   # before subroutine\n";

splice_insert(@a);

print "@a   # after subroutine\n";

[download]

Prints:

0 1 2 3 4 5 6   # before subroutine
0 1 a b c 4 5 6 # after splice
. . . . . . . . # after for loop
. . 2 3 . . .   # after subroutine

[download]

-xdg

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In reply to Re^6: Unobvious Pathological Code Snippets by xdg
in thread Unobvious Pathological Code Snippets by QM

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