in reply to Re: Alternative to bytes::length()
in thread Alternative to bytes::length()

Seems like ne "" is what I was looking for. :)

The !! construct won't work because certain strings with lengths can be false: 

marvin@smokey:~ $ perl -le 'print "true" if !!"0";'
marvin@smokey:~ $ perl -le 'print "true" if !!"1";'
true

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What did you mean by "premature", though?

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Re^3: Alternative to bytes::length()
by BrowserUk (Patriarch) on Dec 23, 2009 at 06:16 UTC
    Seems like ne "" is what I was looking for. :)

    Be careful. Anonymonk's benchmark is conflating an aweful lot of other stuff in with the actual code you are concerned about.

    I believe (but I'm open to correction), this to be a far better benchmark, and it shows a radically different result. It might just set your mind at ease. (Or not!): 

    #!/usr/bin/perl --
use strict;
use warnings;
use Benchmark qw( cmpthese );

# Make bytes:: functions available, but use character semantics.
use bytes ();

our $smileys = "\x{263a}" x 10_000;
our $empty = "\x{263a}"; chop $empty;

cmpthese -1, {   
    bytes => q{
        my $c=0;
        ( bytes::length($empty) or bytes::length($smileys) ) and ++$c 
+for 1 .. 1000;
    },
    utf8 => q{
        my $c=0;
        ( length($empty) or length($smileys) ) and ++$c for 1 .. 1000;
    },
    ord => q{
        my $c=0;
        ( ord( $empty ) or ord( $smileys ) ) and ++$c for 1 .. 1000;
    },
    'ne""' => q{
        my $c=0;
        ( $empty ne '' or $smileys ne '' ) and ++$c for 1 .. 1000;
    },
};

__END__
C:\test>junk8
        Rate bytes   ord  ne""  utf8
bytes 1379/s    --  -72%  -75%  -76%
ord   4992/s  262%    --  -10%  -13%
ne""  5566/s  304%   12%    --   -3%
utf8  5757/s  317%   15%    3%    --

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    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]
[d/l]

      I believe that your 'utf8' case is mostly benchmarking the pulling out of the character count cached in the magic, thus completely missing the original problem. Even if it weren't, I don't see how your benchmark provides any justification for not using eq '' (which perhaps you weren't trying to imply).

      - tye        

[reply]
[d/l]
        I believe that your 'utf8' case is mostly benchmarking the pulling out of the character count cached in the magic, thus completely missing the original problem.

        I was mostly concerned with pointing out that it's important to consider exactly what you're benchmarking.

        I'm also not convinced that there is enough of a description of "the original problem" to say whether I missed or not. I'm finding it quite hard to think of an application where the time taken to obtain the length of a string would be very significant?

        Except maybe when sorting strings by length, at which point the caching would pretty much negate the first-time cost.

        I don't see how your benchmark provides any justification for not using eq ''

        Um...cos I modified the original benchmark and didn't think about it. Having just swapped the 'ne's for 'eq's, it does make a suprising difference. Though I haven't thought through whether that's down the efficiency of the operator or the change to the boolean logic.

        It did surprise me greatly that ord worked out much faster than bytes::length.

        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]

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