in reply to Re: Web Site Mapper
in thread Web Site Mapper

I used to use constant all the time, but not anymore. It requires a relatively recent version of perl, and it loads up a lot of code that isn't really necessary for simple cases. Further, it is rather clunky to use it with anything more complex than a simple scalar constant. For instance, to handle the SITES constant above, I would need to change it to an arrayref and modify the site checking code to derefernce the array. That's extra noise with little appreciable gain. Using a subroutine with an empty prototype (which is what constant does anyway) doesn't add a lot of extra code and it avoids the problems constant creates.

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Note: All code is untested, unless otherwise stated

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Re: Re: Re: Web Site Mapper
by exussum0 (Vicar) on Feb 16, 2004 at 16:48 UTC
    Version 1.0 of constant came out in 1997 so it's not that new :)

    Yes, switching from sub XYZ() to constant requires code changes. But for new development, it's a little clearer the intentions of what your sub is there for and that you aren't insane.

    My version of constant.pm has about 100 lines of perl, with warnings::register using about 25. Not too much for some code clarity if you ask me.


    Play that funky music white boy..
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      We're probably not going to come to an agreement on this.

      Note that a lot of people are still using perl 5.005 (constant.pm was first part of 5.6.0), and it wasn't that long ago that Debian and other GNU/Linux distros started installing something a little more recent by default. IIRC, some FreeBSD system scripts won't run on a more recent perl (this may have changed). So there are still a signifcant number of people out there that aren't even on 5.6.

      When I'm coding on my main job, I use newer features of the language without a care, because I know we run a more recent version of perl. However, this script was meant for public consumption, which means avoiding newer things if possible (admittedly, I should also have used -w instead of use warnings).

      Additional clarity can be gained with a simple # Constants comment above the subroutines in question. I didn't do this in the above code, but it wouldn't hurt.

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      Note: All code is untested, unless otherwise stated

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        constant.pm was first part of 5.6.0

        Not true!

        % /usr/bin/perl -v

This is perl, version 5.005_03 built for i386-freebsd

Copyright 1987-1999, Larry Wall
[...]
% cat c1
#! /usr/bin/perl -wl

use strict;
use constant C => 1;
use constant A => [qw/a b/];
use constant H => {qw/a b/};
print C;
print A;
print A->[0];
print H;
print H->{a};
% /usr/bin/perl c1
1
ARRAY(0x8057c18)
a
HASH(0x8057c3c)
b

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        Prior to 5.005_03, constant hashes and arrays didn't work so well, but scalars did. I think scalar constants go all the way back to 5.000 (perhaps you've been tricked by the use 5.006_00 in the source code of later releases)?

        FreeBSD 5.2 ships with 5.6.1, and I think 4.9 does as well.

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Re^3: Web Site Mapper
by Aristotle (Chancellor) on Feb 16, 2004 at 21:54 UTC

    For instance, to handle the SITES constant above, I would need to change it to an arrayref and modify the site checking code to derefernce the array.

    What are you talking about? You can simply 
    use constant SITES => qw(foo.com bar.com baz.com);

    [download]
    and it'll do what you'd expect.

    Makeshifts last the longest.

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      Ahh, I see what I was thinking of: when defining multiple constants on one line, you have to follow the same rules as hashrefs everywhere else (because that's exactly what you're passing to constant.pm). That means using arrayrefs, even when all you really need is an array. As you demonstrated, that isn't necessary when using a single constant.

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      : () { :|:& };:

      Note: All code is untested, unless otherwise stated

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In Section Code Catacombs