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Re: {3} Using Variables in Path Names

by jeroenes (Priest)
on Nov 28, 2001 at 16:06 UTC ( #128038=note: print w/replies, xml ) Need Help??

in reply to Re: Re: Using Variables in Path Names
in thread Using Variables in Path Names

I think tadman ment 2 things. First of all, with the join method you only have a hard-coded separator in one place. If you want another, just replace that one, or better, define a variable for that.

Two, you'd better assign variables, or arrays, to define the subdirectories node for node. That way, the code gets more readible (less comments needed) and better maintainable.


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Re: Re: {3} Using Variables in Path Names
by dragonchild (Archbishop) on Nov 28, 2001 at 19:09 UTC
    This is actually an interesting discussion. Let's take a look at the code for this:
    # Having defined $HOME, $first, $second up above somewhere... # Using interpolation my $dir = "$HOME/$first/$second"; # vs. Using join my $dir = join '/', ($HOME, $first, $second);
    Personally, I find the first to be more expressive. It tells me, the reader, that you're talking about a directory structure because that's how I'm used to seeing it.

    join, to me, talks about creating generic strings, usually for some cryptic file using comma-delimitation or as a way of printing out an array in a readable form.

    Now, this is all personal style. I guess I'm just used to seeing it that way.

    As for speed ... I haven't done the Benchmarking, but I think that interpolation might actually even be faster.

    As for usability, I will agree that it's easier to manipulate a list vs. manipulating a string, but that usually doesn't really matter. Most of the time, you're manipulating said string in a recursive fashion. So, you're just adding vs. adding & subtracting (which you'd have to do if you converted the recursion to a loop).

    We are the carpenters and bricklayers of the Information Age.

    Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.

      My 0.02.

      I don't like both variants. They are not portable. It is better to use File::Spec for operations on filenames:

      use File::Spec; my $dir = File::Spec->catdir($HOME, $first, $second);
      I suppose my rationale behind using join over string interpolation was that when working with directories, it is often advantageous to use an array instead of a string. This way you can resolve path components like '..' using pop instead of a regex. The other idea was that each piece supplied to the join would represent a single path component, which could be validated using a quick map for the extra paranoid. Of course, then $HOME would have to be split into something like @HOME.

      Anyway, Benchmark says:
      Benchmark: timing 1000000 iterations of interpolator, joiner... interpolator: 5 wallclock secs ( 5.13 usr + 0.00 sys = 5.13 CPU) @ +194931.77/s (n=1000000) joiner: 4 wallclock secs ( 4.53 usr + 0.00 sys = 4.53 CPU) @ 22 +0750.55/s (n=1000000) Rate interpolator joiner interpolator 194932/s -- -12% joiner 220751/s 13% --
      #!/usr/bin/perl my ($the,$fastest,$donut,$youve,$ever,$seen) = qw [ the fastest donut +you've ever seen ]; sub joiner { my $x = join ('/', $the,$fastest,$donut,$youve,$ever,$seen); } sub interpolator { my $x = "$the/$fastest/$donut/$youve/$ever/$seen"; } use Benchmark qw [ cmpthese ]; cmpthese ( 1000000, { joiner => \&joiner, interpolator => \&interpolator, } );
      As far as I can tell, using 'join' or the concatenation operator(.) are both reasonably fast; interpolation is slower than either. Of course, you would have to do a lot of joining for it to make any difference in the speed of your program.
      If interpolation is more readable (which I think it is), you could always do this:
      my $dir = $HOME.'/'.$first.'/'.$second;

      for the extra speed boost. :-)
      (Actually, that's kind of ugly, too. I would probably just interpolate.)

      Impossible Robot

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