Inspired by Tim and Sam's work, I've just been having a play with xh_prof.

I noticed that in admin_category we use $this->category_cache to cache records.

This is a protected variable, which is set to an array in the constructor, and also in a purge function. The only operations on it are:

• $this->category_cache = array();
• isset($this->category_cache[$key])
• $this->category_cache[$key] = $value;
• return $this->category_cache[$key];
• while($this->category_cache)
• array_pop($this->category_cache);

In every function which accesses it, we still call is_array($this->category_cache) even though it is only every treated as an array.

On a default install of Moodle with no additional plugins, the locate() function is called around about 8,600 times with up to two is_array() calls.

By removing this, I'm seeing savings of around about 100ms on my laptop.