dom111.co.uk » Ruby

String Variable Concatenation

dom111 — Fri, 14 Aug 2009 13:27:09 +0000

I stumbled across something odd today in PHP:

$r = '';
$r .= $r .= $r .= 'a';

Now, personally, I’d have expected a syntax error from the above code, but the result was even more confusing at first…

print $r; // 'aaaa'

Not sure if this was the expected output or not I tested similar code in other languages:

Ruby:

r = ''
r += r += r += 'a'
puts r # 'a'

Python:

r = ''
r += r += r += 'a'
#   File "", line 1
#     r += r += r += 'a'
#             ^
# SyntaxError: invalid syntax

Javascript:

var r = '';
r += r += r += 'a';
alert(r); // 'a'

Perl:

my $r = '';
$r .= $r .= $r .= 'a';
print $r; // 'aaaa'

That explains it!

So the reason the string is ‘aaaa’ seems to be that the code is evaluated from right to left:

$r = '';
$r += $r += $r += 'a';
 
// How it works:
//
// $r += 'a'; // 'a'
// $r += $r += 'a'; // 'a' + 'a';
// $r += $r += $r += 'a'; // 'aa' + ('a' + 'a')

I don’t think it’s a bug, well, at least I assume not, but is there a name for this?

Update: I asked some clever people for help understanding it.

chunk – Read a large (XML) file a chunk at a time

dom111 — Fri, 10 Jul 2009 12:35:28 +0000

I’ve recently had to parse some pretty large XML documents, and needed a method to read one element at a time.

Here’s a fairly simple solution in PHP and Ruby form (hopefully a Python one coming soon…).

If you have the following file (complex-test.xml):

 version="1.0" encoding="UTF-8"?>
>
  >
    >Title 1>
    >It's name goes here>
    >
      >>
      >>
      >>
      >>
    >
    >>
  >
  >>
  >
    >>
    >>
  >
  >>
  >>
>

And wanted to return the s

PHP:

require_once('class.chunk.php');
 
$file = new Chunk('complex-test.xml', array('element' => 'Object'));
 
while ($xml = $file->read()) {
  $obj = simplexml_load_string($xml);
  // do some parsing, insert to DB whatever
}

Ruby:

require 'chunk.rb'
 
file = Chunk.new('complex-test.xml', { 'element' => 'Object' })
 
while xml = file.read
  doc = REXML::Document.new(xml)
  // do some parsing, blah...
end

It (probably) doesn’t work with nested XML elements, but the use I had for it didn’t require that it did.

You can get the PHP version here, and the Ruby one here.

Update: The class was accepted onto PHP Classes as a notable package! 04/08/2009.

Ruby on Rails: image_submit_tag and :confirm

dom111 — Thu, 14 Aug 2008 17:10:00 +0000

I was told about an issue today with the image_submit_tag not supporting the :confirm method on the element:

1	<%= image_submit_tag('buttons/submit.gif', { :confirm => 'Are you sure?' }) %>

so I thought I’d share a quick fix which would be the actual javascript returned by the function:

1 2	<%= image_submit_tag('buttons/submit.gif', { :onclick => 'return confirm(\'Are you sure?\');' }) %>

Hope this can save some people time…