---+ Package =TWiki::Prefs::PrefsCache=

The PrefsCache package holds a cache of topics that have been read in, using
the TopicPrefs class.  These functions manage that cache.

We maintain 2 hashes of values:
   * {locals} Contains all locals at this level. Locals are values that
     only apply when the current topic is the topic where the local is
     defined. The variable names are decorated with the locality where
     they apply.
   * {values} contains all sets, locals, and all values inherited from
     the parent level

As each cache level is built, the values are copied down from the parent
cache level. This sounds monstrously inefficient, but in fact perl does
this a lot better than doing a multi-level lookup when a value is referenced.
This is especially important when many prefs lookups may be done in a
session, for example when searching.


%TOC%

---++ ClassMethod *new* <tt>($prefs,$parent,$type,$web,$topic,$prefix)</tt>

Creates a new Prefs object.
   * =$prefs= - controlling TWiki::Prefs object
   * =$parent= - the PrefsCache object to use to initialise values from
   * =$type= - Type of prefs object to create, see notes.
   * =$web= - web containing topic to load from (required is =$topic= is set)
   * =$topic= - topic to load from
   * =$prefix= - key prefix for all preferences (used for plugins)
If the specified topic is not found, returns an empty object.



---++ ObjectMethod *finalise* <tt>($parent)</tt>

Finalise preferences in this cache, by freezing any preferences
listed in FINALPREFERENCES at their current value.
   * $parent = object that supports getPreferenceValue



---++ ObjectMethod *loadPrefsFromTopic* <tt>($web,$topic,$keyPrefix)</tt>

Loads preferences from a topic. All settings loaded are prefixed
with the key prefix (default '').



---++ ObjectMethod *loadPrefsFromText* <tt>($text,$meta,$web,$topic)</tt>

Loads preferences from text and optional metadata. All settings loaded
are prefixed with the key prefix (default ''). If =$meta= is defined,
then metadata will be taken from that object. Otherwise, =$text= will
be parsed to extract meta-data.



---++ ObjectMethod *insert* <tt>($type,$key,$val)</tt>

Adds a key-value pair of the given type to the object. Type is Set or Local.
Callback used for the Prefs::Parser object, or can be used to add
arbitrary new entries to a prefs cache.

Note that attempts to redefine final preferences will be ignored.



---++ ObjectMethod *stringify* <tt>($html,\%shown) -> $text</tt>

Generate an (HTML if $html) representation of the content of this cache.