in reply to Re^2: Puzzled by value of $overload::ops{binary}
in thread Puzzled by value of $overload::ops{binary}

I'd suggest PDL is the ultimate operator-overloader "source of truth". Mutating overloads is implemented in PDL::Ops, specifically (https://github.com/PDLPorters/pdl/blob/ad2783ad4b00583f14af3a3c24a93bb9f1a4ff33/Basic/Ops/ops.pd#L191-L196): 
    $ret .= pp_line_numbers(__LINE__, <<EOF) if $mutator;
BEGIN {
# in1, in2, out, swap if true
\$OVERLOADS{'$op='} = sub { PDL::$name(\$_[0]->inplace, \$_[1]); \$_[0
+] };
}
EOF

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Modifying the generated code for += to this: 
#line 192 "ops.pd"
BEGIN {
# in1, in2, out, swap if true
$OVERLOADS{'+='} = sub {
use Carp; use Test::More; diag "RUN ", Test::More::explain \@_;
PDL::plus($_[0]->inplace, $_[1]); $_[0] };
}

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and running it like this: 
$ perl -MPDL -e '$p=pdl(1); $p+=2'

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gives: 
# RUN [
#   bless( do{\(my $o = '94749946365136')}, 'PDL' ),
#   2,
#   undef
# ]

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so your XS function should work. Did you make an overload for +=?

Replies are listed 'Best First'.
Re^4: Puzzled by value of $overload::ops{binary}
by syphilis (Archbishop) on Jun 25, 2024 at 14:38 UTC
    In Math::GMPz, the overloading of '++' is: 
    void overload_inc(pTHX_ SV * p, SV * a, SV * b) {
     mpz_add_ui(*(INT2PTR(mpz_t *, SvIVX(SvRV(p)))), *(INT2PTR(mpz_t *
+, SvIVX(SvRV(p)))), 1);
}

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    which is simply doing p = p + 1, with "p" being a Math::GMPz object.
    Then, in the bottom section of the XS file I have: 
    void
overload_inc (p, a, b)
    SV *    p
    SV *    a
    SV *    b
        CODE:
        overload_inc(aTHX_ p, a, b);
        XSRETURN_EMPTY; /* return empty stack */

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    Works fine.
    For the overloading of '+=', it gets a bit drawn out because we might be adding on something other than an IV.
    But if we were just dealing with adding on an unsigned long int we would actually have: 
    SV * overload_add_eq(pTHX_ SV * p, SV * a, SV * b) {
     mpz_add_ui(*(INT2PTR(mpz_t *, SvIVX(SvRV(p)))), *(INT2PTR(mpz_t *
+, SvIVX(SvRV(p)))), SvUV(a));
     SvREFCNT_inc(p);
     return p;
}

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    which is just doing p = p + a, and returning p (after increasing the refcount).
    The corresponding code in the bottom section of the XS file would be: 
    SV *
overload_add_eq (p, a, b)
    SV *    p
    SV *    a
    SV *    b
CODE:
  RETVAL = overload_add_eq (aTHX_ p, a, b);
OUTPUT:  RETVAL

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    Now, it's not hard to work out what that overload_add_eq() would look like if I were to apply the same approach as used by overload_inc(): 
    void overload_add_eq(pTHX_ SV * p, SV * a, SV * b) {
     mpz_add_ui(*(INT2PTR(mpz_t *, SvIVX(SvRV(p)))), *(INT2PTR(mpz_t *
+, SvIVX(SvRV(p)))), SvUV(a));
}

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    and 
    void
overload_add_eq (p, second, third)
    SV *    p
    SV *    a
    SV *    b
        CODE:
        overload_add_eq(aTHX_ p, a, b);
        XSRETURN_EMPTY; /* return empty stack */

    [download]
    But I've never managed to get that to work.
    It has, however, been a while since I've tried - so I'll have another crack at it tomorrow (as it's now getting late over here) and see if I can get lucky.
    (I can't actually remember just what the problem is.)

    BTW, I've fiddled about with that code that I've posted, so it might contain one or more typos.

    Cheers,
    Rob
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      .... so I'll have another crack at it tomorrow ....

      In GMPz.xs, in the bottom section of the file I have replaced: 
      SV *
overload_add_eq (a, b, third)
    SV *    a
    SV *    b
    SV *    third
CODE:
  RETVAL = overload_add_eq (aTHX_ a, b, third);
OUTPUT:  RETVAL

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      with 
      void
overload_add_eq (a, b, third)
    SV *    a
    SV *    b
    SV *    third
        CODE:
        overload_add_eq (aTHX_ a, b, third);
        XSRETURN_EMPTY; /* return empty stack */

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      And in the top section of the file I have replaced: 
      SV * overload_add_eq(pTHX_ SV * a, SV * b, SV * third) {
    /* lengthy code  snipped */
}

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      with 
      void overload_add_eq(pTHX_ SV * a, SV * b, SV * third) {
     PERL_UNUSED_ARG(third); /* UPDATE: This line can be removed as ir
+relevant */
     mpz_add_ui(*(INT2PTR(mpz_t *, SvIVX(SvRV(a)))), *(INT2PTR(mpz_t *
+, SvIVX(SvRV(a)))), SvUV(b));
}

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      This means that we're always adding SvUV(b) to a, irrrespective of what b actually is.
      This is good enough for demonstration purposes if we make sure that the second arg (b) is an IV, but we probably don't want to run make test.

      On Windows 11, perl-5.38.0, I then run perl Makefile.PL, followed by make.
      The build emits no warnings.
      Then: 
      > perl -Mblib -MMath::GMPz -MDevel::Peek -wle "$x = Math::GMPz->new(12
+34); $x++;print $x; $x += 15; print $x; Dump($x);"
1235
Use of uninitialized value $x in print at -e line 1.

SV = PVIV(0x1abd93865e0) at 0x1abdad3ae48
  REFCNT = 1
  FLAGS = ()
  IV = 1837594613288
  PV = 0

      [download]
      As you can see from that, the Math::GMPz object ($x) has been well and truly clobbered by the '+=' overloading.
      Anyone interested can try this out by making the above alterations to GMPz.xs in https://cpan.metacpan.org/authors/id/S/SI/SISYPHUS/Math-GMPz-0.61.tar.gz.
      Thoughts, observations, opinions and revelations are all most welcome.

      UPDATE: I see the same behaviour on Cygwin, and also on Ubuntu-22.04.4-LTS.

      UPDATE 2: I'll also point out that this altered version of overload_add_eq() works as expected when called as a function:
      > perl -Mblib -MMath::GMPz -MDevel::Peek -wle "$x = Math::GMPz->new(12
+34); $x++; print $x; Math::GMPz::overload_add_eq($x, 15, 0); print $x
+;"
1235
1250

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      UPDATE 3: Also, if I remove the '+=' overloading (by commenting out the appropriate line in GMPz.pm), then the '+=' overloading (which then uses the '+' overloading) works fine:
      > perl -Mblib -MMath::GMPz -MDevel::Peek -wle "$x = Math::GMPz->new(12
+34); $x++;print $x; $x += 15; print $x; Dump($x);"
1235
1250
SV = IV(0x2bfffa61b78) at 0x2bfffa61b88
  REFCNT = 1
  FLAGS = (ROK)
  RV = 0x2bfff38aac8
  SV = PVMG(0x2bfffa24a58) at 0x2bfff38aac8
    REFCNT = 1
    FLAGS = (OBJECT,IOK,READONLY,pIOK)
    IV = 3023652457216
    NV = 0
    PV = 0
    STASH = 0x2bfffa5e5e8       "Math::GMPz"

      [download]
      Cheers,
      Rob
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        I'd add some debugging checks in overload_add_eq to see what state the SVs are in when they arrive in it. Also, as a matter of good practice, I would keep all the SV-mangling stuff in the XS function, and just pass to your C function the mpz_t (or a pointer) values. If that meant the C functions you've shown here go away, then so be it.
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