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Re: How do I insert a line into a file?

by Juerd (Abbot)
on Mar 31, 2002 at 14:44 UTC ( #155606=note: print w/replies, xml ) Need Help??

in reply to How do I insert a line into a file?

Dominus, you have again created a GREAT module, and I will surely put it to use very often.

A string cannot be used to store data structures, unless serialized. It would however be great to use this efficient Tie::File together with array or hash references. Because putting the serialization in Tie::File would ruin all non-serializing operation, I thought it would be nice to tie an array and have automatic serialization. I have searched CPAN, but couldn't find a module that does what I want, so I created this quick hack:

package Tie::FreezeThaw; # NOTE: # This is a quick hack and has NOT been tested thoroughly! # NOTE: # You can't use the elements directly as references! # (if @xyzzy is tied, $xyzzy[1][2] won't work. # Use $foo = $xyzzy[1]; $foo->[2] instead.) use FreezeThaw qw(freeze thaw); use base 'Tie::Array'; use strict; sub TIEARRAY { bless $_[1], $_[0] } sub FETCHSIZE { scalar @{ $_[0] } } sub STORESIZE { @{ $_[0] } = $_[1] } sub EXISTS { exists $_[0]->[$_[1]] } sub DELETE { delete $_[0]->[$_[1]] } sub STORE { ($_[2] = freeze $_[2]) =~ s/([^\x20-\x7E])/sprintf "\xFF%02x", $1/ +ge; $_[0]->[$_[1]] = $_[2]; } sub FETCH { (my $foo = $_[0]->[$_[1]]) =~ s/\xFF(..)/chr hex $1/ge; return (thaw $foo)[0]; } 1;
Which allows me to use Tie::File with complexer data structures (of course, entire records will be overwritten, but that's still more efficient than re-writing the entire file) without having to think about the serialization.

use Tie::File; use Tie::FreezeThaw; use strict; tie my @foo, 'Tie::File', 'testfile' or die $!; tie my @bar, 'Tie::FreezeThaw', \@foo; push @bar, [ qw/1..10/ ];
(If there's already a module like my quick Tie::FreezeThaw hack, please let me know)


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[erix]: Look what I found! :P
[Corion]: Hmm - actually, I don't need them, even though they'd be nice. I just want the (say) 10 latest images, and that's easily done with a limit 10 offset 0 clause, as I don't need all top 10 images for all users.
[Corion]: erix: Sure, but this is for a really-lightweight application and I'm replacing a CSV file / JSON file for user configuration with SQLite (and optionally, Pg) :)
[erix]: isn't a texty format handier for configs?
[Corion]: So far, I've avoided having even a user database by storing the user information in a (signed) cookie that the browser keeps for me, but as I want to be able to lock users, I need a second storage option :)
[Corion]: erix: It's needed for keeping the list of users and the list of tags associated with an image, and for keeping the images with users. I want an easy way to know if an image can be deleted, which means that it can't be referenced by any tag anymore. ...
[Corion]: SQL feels like a natural choice here :)

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