The
proplib library provides an abstract interface for creating and manipulating property lists. Property lists have object types for boolean values, opaque data, numbers, and strings. Structure is provided by the array and dictionary collection types.
Property lists can be passed across protection boundaries by translating them to an external representation. This external representation is an XML document whose format is described by the following DTD:
http://www.apple.com/DTDs/PropertyList-1.0.dtd
Property container objects are reference counted. When an object is created, its reference count is set to 1. Any code that keeps a reference to an object, including the collection types (arrays and dictionaries), must “retain” the object (increment its reference count). When that reference is dropped, the object must be “released” (reference count decremented). When an object's reference count drops to 0, it is automatically freed.
The rules for managing reference counts are very simple:
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If you create an object and do not explicitly maintain a reference to it, you must release it.
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If you get a reference to an object from other code and wish to maintain a reference to it, you must retain the object. You are responsible for releasing the object once you drop that reference.
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You must never release an object unless you create it or retain it.
Object collections may be iterated by creating a special iterator object. Iterator objects are special; they may not be retained, and they are released using an iterator-specific release function.