in reply to Alternative to bytes::length()

Sometimes, I wish for a boolean context... (It would be great for grep too.) Or maybe the character length should be stored in string variables?

I can't think of any replacement short of turning off the flag, calling length, then restoring it.

What's the problem with the current solution? 

require bytes;
sub emptystr(_) {
    no warnings 'uninitialized';
    return !bytes::length($_[0]);
}

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By the way, 

use bytes; 
no bytes;

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is equivalent to 

use bytes ();

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There's also similar 

require bytes;

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Replies are listed 'Best First'.
Re^2: Alternative to bytes::length()
by creamygoodness (Curate) on Dec 23, 2009 at 01:38 UTC
    Or maybe the character length should be stored in string variables?

    I think the length in characters might be cached using MAGIC -- I know some UTF-8 stuff is.

    What's the problem with the current solution?

    There was just a post to p5p from someone who wanted to terminate the bytes pragma with extreme prejudice. I wanted to mention this use case.

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      Do you have an example of this magic?

      That would be an argument for creating a new function, not for keeping bytes.

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        Actually, simply calling length on a scalar with UTF8=1 adds the magic. 
        >perl -MDevel::Peek -e"Dump $_=chr(0x2660)x100; length $_; Dump $_"
SV = PV(0x2379ec) at 0x1845eec
  REFCNT = 1
  FLAGS = (POK,pPOK,UTF8)
  PV = 0x184c5ec "..."\0 [UTF8 "..."]
  CUR = 300
  LEN = 304
SV = PVMG(0x18242cc) at 0x1845eec
  REFCNT = 1
  FLAGS = (SMG,POK,pPOK,UTF8)
  IV = 0
  NV = 0
  PV = 0x184c5ec "..."\0 [UTF8 "..."]
  CUR = 300
  LEN = 304
  MAGIC = 0x1824e64
    MG_VIRTUAL = &PL_vtbl_utf8
    MG_TYPE = PERL_MAGIC_utf8(w)
    MG_LEN = 100         <---------- char length

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        It's a pity that actions such as chop, appending a UTF8=0 string, etc void the count instead of updating it.

        Note that $_ eq '' doesn't add the magic, so not only is it faster, it uses less memory.

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        Looks like you found the caching mechanism. From perlguts: 
          w  PERL_MAGIC_utf8           vtbl_utf8       UTF-8 length+offset cac
+he

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        As for keeping bytes... meh, my attachment to the bytes pragma extended only to that use case, as the efficiency of CORE::length() with SVf_UTF8 scalars is a bummer. I'm not even going to bother posting to p5p now that my concern has been addressed another way.

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      Why would they eliminate the bytes pragma? What about those of us who aren't always manipulating character data and actually do care about the bytes themselves?
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        Strings can contain bytes. You don't have to do anything special to work with bytes. use bytes; has nothing to do with manipulating bytes.

        If you need to manipulate the internal string format to optimize or to work with some buggy XS,
        You want utf8::upgrade or utf8::downgrade.
        If you need you need to encode to UTF-8 or decode from UTF-8,
        You want utf8::encode, Encode::encode, utf8::decode or Encode::decode.

        The person probably wants to eliminate it because of that very misconception you expressed. But don't worry, if anything is ever done, it would still be available on CPAN.

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