Saturday, October 15, 2011

Concentration and Flow or Yet Another Dependency Injection Note

Imagine that you need to do some small home improvement or maintenance work and you have all the needed tools, in good quality, clean and well maintained with all cutting blades sharpened and no missing screwdriver heads. A nice feeling - isn't it? When you start work like this you can concentrate on the task at hand instead of thinking where you can borrow that drill tool.

Collaborators in an algorithm are like those tools, having them readily available lets you concentrate on the problem.

Friday, October 14, 2011

Object oriented versus functional interface

I use DateTime::Format::W3CDTF for parsing my dates:

my $w3c = DateTime::Format::W3CDTF->new;
my $dt = $w3c->parse_datetime( $date_string );

I wish it was:

my $dt = DateTime::Format::W3CDTF->parse_datetime( $date_string );

and that the library created the parser on the fly as needed. It's not only less typing - but also much simpler mental model. This simpler model is sometimes too simple - for example if you parse a lot of dates then sparing the parser creation each time can make a difference.

I think the optimal thing to do is provide two APIs - like JSON - a functional one:

$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;

and an object oriented one:

$json = JSON->new->allow_nonref;
$perl_scalar = $json->decode( $json_text );

for those that need that extra control.

Monday, October 03, 2011

open expects filename as binary data encoded in the system characterset

I guess this is not a surprise to anyone who thought about how this is supposed to work, but for the sake of being systematic, here is the code:
use strict;
use warnings;
use autodie;
use HTML::Entities;
use Encode;

my $a = HTML::Entities::decode( 'ñ' );

open(my $fh, '>', $a );
print $fh "Without encoding\n";
close $fh;

open(my $fh1, '>', encode( 'UTF-8', $a ) );
print $fh1 "With encoding\n";
close $fh1

And here is the result when run on an system with UTF8 locales:
zby@zby:~/myopera/tmp$ ls
? ñ
zby@zby:~/myopera/tmp$ cat ñ
With encoding

'' is the name of the script itself, the mark '?' hides the F1 hexadecimal code and that file contains 'Without encoding'.