in reply to Re^5: XS: returning a 64-bit unsigned int?
in thread XS: returning a 64-bit unsigned int?

That is how it's done. A single SvGETMAGIC if you read a scalar, no matter how many times you read it. A single SvSETMAGIC if you write to a scalar, no matter how many times you write to it.

And if you're processing a real array containing a million real scalars, then that's 2 million redundant, time consuming function calls conditional tests.

Addition: Were it possible to perform a single test on the array to detect magic, it might be worth doing to allow me to gracefully reject it. But as is, the only sensible option is to document that only real arrays of real scalars are acceptable input and fail noisily if I am given anything else.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
  • Comment on Re^6: XS: returning a 64-bit unsigned int?

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Re^7: XS: returning a 64-bit unsigned int?
by ikegami (Patriarch) on Sep 27, 2011 at 18:00 UTC

    If they're redundant, don't do them. Generally speaking, though, they're not redundant. The outcome of each test is independent of the others. Magic can be tied to an element without being tied to the array, and the use of GET and SET magic is independent. 

    $ perl -MDevel::Peek -E'
   sub TIESCALAR { bless \my $x; }
   sub FETCH { 3 }
   my @a = (6,7);
   tie $a[1], __PACKAGE__;
   say $a[0];
   say $a[1];
   Dump(\@a);
'
6
3
SV = IV(0x9a22324) at 0x9a22328
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x9a3c2e8
  SV = PVAV(0x9a23174) at 0x9a3c2e8
    REFCNT = 2
    FLAGS = (PADMY)
    ARRAY = 0x9a3af28
    FILL = 1
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)
    Elt No. 0
    SV = IV(0x9a21764) at 0x9a21768
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 6
    Elt No. 1
    SV = PVMG(0x9a64d50) at 0x9a21898
      REFCNT = 1
      FLAGS = (GMG,SMG,RMG,pIOK,pPOK)
      IV = 3
      NV = 0
      PV = 0x9a370d0 "3"\0
      CUR = 1
      LEN = 12
      MAGIC = 0x9a46460
        MG_VIRTUAL = &PL_vtbl_packelem
        MG_TYPE = PERL_MAGIC_tiedscalar(q)
        MG_FLAGS = 0x02
          REFCOUNTED
        MG_OBJ = 0x9a22258
        SV = IV(0x9a22254) at 0x9a22258
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0x9a4f4a0

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[reply]
[d/l]
      Magic can be tied to an element without being tied to the array.

      I know. That's why it is so expensive to cater for.

      The fact that almost no one uses tied scalars for anything makes it all the worse.

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]

        Tie is only one kind of magic. Magic scalars are actually quite common. 

        $1
$|
$ENV{PATH}
$ISA[0]
$tied{$k}
$tied[$i]
$#a
pos
substr

        [download]

        (Some of these only return magical scalars in lvalue context.)

        Every tied hash and array uses them in order to call STORE on the hash or array when assigning to the scalar returned by $tied{$i} and $tied[$i].

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