Section 14: Persistence

• 14.1 Levels of Persistence
• 14.1.1 A Note About Terminology
• 14.1.2 About the Examples in this Section
• 14.2 No Persistence
• 14.3 Simple Persistence
• 14.3.1 Two Examples of Simple Persistence
• 14.4 Isomorphic Persistence
• 14.4.1 Isomorphic versus Simple Persistence
• 14.4.2 Isomorphic Persistence of a Tools.h++ Class
• 14.4.3 Designing Your Class to Use Isomorphic Persistence
• 14.4.4 Writing rwSaveGuts and rwRestoreGuts Functions
• 14.4.5 Isomorphic Persistence of a User-designed Class
• 14.5 Polymorphic Persistence
• 14.5.1 Operators
• 14.5.2 Designing your Class to Use Polymorphic Persistence
• 14.5.3 Polymorphic Persistence Example
• 14.6 A Few Friendly Warnings
• 14.6.1 Always Save an Object by Value before Saving the Identical Object by Pointer
• 14.6.2 Don't Save Distinct Objects with the Same Address
• 14.6.3 Don't Use Sorted RWCollections to Store Heterogeneous RWCollectables
• 14.6.4 Define All RWCollectables That Will Be Restored

Persistence is the ability to save an object to a file or a stream and then restore that object from the file or stream. Persistence is a very important feature of objects because it facilitates the exchange of objects between processes. Using persistence and working through streams, you can send objects from one program to another, or from one user to another. You can also save a persistent object to a file on a disk, and restore it from disk at another time, or in another place.