Smarty caching components - php

Question

The Smarty FAQ suggests one way to handle cacheable fragments, but it needs each page controller to do tons of work up-front, instead of encapsulating things properly.
We want to get to a stage where we can do something like:
<div id="header">
{our_categories}
{our_subcategories category=$current_category}
</div>
The output of the our_ prefixed functions should be completely cacheable, only relying on the named parameters (if any.) If we referred to {our_categories} in more than one template, they should all refer to the same cached content.
(it's probably worth mentioning that we tried using {insert name="..."} and coding up our own functions, but the results weren't cacheable, and we ended up hand-cranking the HTML retunred, rather than benefiting from Smarty's template processing.)
Our first crack at this uses a custom function smarty_function_our_categories, but the caching's going horribly wrong. Here's what our function looks like:
function smarty_function_our_categories($params, &$smarty) {
$smarty->caching = 2;
$smarty->cache_lifetime = 3600; # 1 hour
if (!$smarty->is_cached(...)) {
// ... do db access to fetch data for template...
$smarty->assign(....);
}
return $smarty->fetch(...);
}
The problem is: calling $smarty->fetch() within a function confuses smarty, making it lose track of which templates have insert-tags, and which don't. The end result is that Smarty forgets to replace certain markers when serving up cached content (markers it puts there to say: "replace this with the results of some non-caching {insert ...} call.) In our case, this manifests itself with our site showing a couple of md5 checksums and a php-serialized memento where our main menu should be - that's not good.
We assume we've made a mistake in how we're building our components, so the question finally becomes:
How do you safely create a caching component using Smarty to render itself?

Answer 1

You should not change caching parameters from inside Smarty function. Wheither or not the result of the plugin output is cacheable is defined when you register plugin.
http://www.smarty.net/manual/en/caching.cacheable.php
To create uncachable content inside cachable template just use {dynamic} blocks like this:
//Registering dynamic non-caching block with Smarty
$template->register_block('dynamic', 'smarty_block_dynamic', false);
function smarty_block_dynamic($param, $content, &$smarty) {
return $content;
}