Variable access to array index

[clphillips]

Assume the following:

$arr = array(
    array('x' => 0),
    array('x' => 1),
    array('x' => 2),
    array('x' => 3),
);

$b = array(1, 2, 3, 4);

{% for a in arr %}
    {{ b.{{ a.x }} }}

{% endfor %}

Expected output:

1
2
3
4

Actual output: unexpected character in filters : "." at 306 on line 228 in /h2o/h2o/parser.php

(edited to clarify variable tags)

[superdaigo]

The next template's syntax was wrong.

{{ b.{{ a.x }} }}

You can use nested "for" tag instead of nested "{{ }}" tag like below or prepare ordered $b array in php code.

<ul>
{% for a in arr %}
    {% for i, b_val in b %}
        {% if i == a.x %}
            <li>{{ b_val }}</li>
        {% endif %}
    {% endfor %}
{% endfor %}
</ul>

[clphillips]

Thanks superdaigo. The example you provided works, however it is extremely inefficient (O(n^2): nested loop, can't break after item found).

Here's what I'm looking for in PHP for comparison:

foreach ($arr as $a) {
    echo $b[$a['x']];
}

[superdaigo]

Hi, clphillips.
It's true that the nested "for loop" is inefficient and deep nest was evil.
If you worry about the efficiency, here is two solutions.

1. Create ordered variables before render to template.

   $arr = array(
       array('x' => 0),
       array('x' => 1),
       array('x' => 2),
       array('x' => 3),
   );
   
   $b = array(1, 2, 3, 4);
   // prepare
   $b_ordered = array();
   foreach ($arr as $a) {
       $b_ordered[] = $b[$a['x']];
   }
   // render
   h2o->render(array( 'b_new' => $b_ordered ));

   {% for b_val in b_new %}
     {{ b_val }}
   {% endfor %}

2. Create custom tags or extensions.
   ... It's not easier than above and probably too much ...

The "h2o" is fast and simple template engine. I think something complex should be done in PHP code.

[clphillips]

Thanks again superdaigo.

You solution in #1 is exactly what I did as a work around. I'm still concerned with it, because if you analyze the run time (PHP + h2o) it's still a nested loop (O(n^2)). However, it gets the job done and keeps the template simple and easy to understand (which is why we chose h2o to begin with). :)