I keep looking at this piece of overload.pm documentation: 
    *    *Assignments*

             +=  -=  *=  /=  %=  **=  <<=  >>=  x=  .=
             &=  |=  ^=  &.=  |.=  ^.=

         [snip]

         The subroutine for the assignment variant of an operator is
         required only to return the result of the operation.

[download]
That seems to me to be asserting that these operations (unlike '++' and '--') do require a value to be returned.
And it also looks to me that overload.pm is somehow enforcing that policy.

This following rewrite of the simplified overload_add_eq C and XS functions works fine: 
void overload_add_eq(pTHX_ SV * a, SV * b, SV * third) {
     dXSARGS;
     PERL_UNUSED_ARG(third);
     mpz_add_ui(*(INT2PTR(mpz_t *, SvIVX(SvRV(a)))), *(INT2PTR(mpz_t *
+, SvIVX(SvRV(a)))), SvUV(b));
     XSRETURN(1);
}

[download]
and 
void
overload_add_eq (a, b, third)
    SV *    a
    SV *    b
    SV *    third
        CODE:
        overload_add_eq (aTHX_ a, b, third);
        XSRETURN(1);

[download]
But I wonder if that achieves anything significant over the implementation that has been working fine for the last umpteen years.

Anyway, I don't want to get too bogged down in this - though it's certainly interesting enough to encourage a bit more investigation.

Cheers,
Rob

In reply to Re^7: Puzzled by value of $overload::ops{binary} by syphilis
in thread Puzzled by value of $overload::ops{binary} by syphilis

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.