Re^4: XS: returning a 64-bit unsigned int?

[BrowserUk]

There is a SvIsUV_on(sv)

Not in the docs I'm looking at. Where did you dig that one up from?

and you didn't handle magic. If it's just an internal scalar, you could get away with not doing those,

No, I never handle magic. It's not laziness but a design choice. The reason I drop into XS/I::C is for performance. There is no point in doing that if you then allow people to pass you arrays that are tied to disk, or scalars that use post-its as backing store :)

IMO the way perl handles magic in-line, is all wrong anyway. It imposes huge costs for something that is actually quite a rare event. It ought to be possible to make a single determination at the top of a routine and defer to a separate routine that handles magic when needed, thus leaving the main-line code free of such considerations. But that's another wish list item that it's far too late to consider at this point.

[ikegami]

It ought to be possible to make a single determination at the top of a routine

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. You don't want to call magic twice, and not just for performance reasons.

[BrowserUk]

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.

[ikegami]

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