Actually, the odd operator is =, not +=. Most operators will dictate the context of their operands, and so does +=: both operands are in scalar context. But = is special cased, there the operands could be either in list or scalar context - and it's the left operand that decides.

The following program might be of interest: 

#!/usr/bin/perl

use strict;
use warnings;

my ($a, @a) = ("");

sub foo : lvalue {
    print wantarray ? "LIST:   " : "SCALAR: ";
          wantarray ?  @a        :  $a
}

 foo ()   = 1; print "\$a = $a; \@a = [@a]\n";
(foo ())  = 2; print "\$a = $a; \@a = [@a]\n";
 foo ()  += 3; print "\$a = $a; \@a = [@a]\n";
(foo ()) += 4; print "\$a = $a; \@a = [@a]\n";

__END__
SCALAR: $a = 1; @a = []
LIST:   $a = 1; @a = [2]
SCALAR: $a = 4; @a = [2]
SCALAR: $a = 8; @a = [2]

[download]

Abigail

In reply to Re: Fringe case slice behavior by Abigail-II
in thread Fringe case slice behavior by davido

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.