They're functional! They're efficient!!
summary
Persistent data structures keep old versions intact while reusing unchanged parts to save time and memory, implemented as trees (tries) that copy only nodes on the path to a changed leaf rather than whole arrays. That yields structural sharing, far fewer copies than naive immutability, and update cost tied to tree depth not length (useful with branching factors like 32). JavaScript options mentioned include mori (a ClojureScript port) and Immutable.js from Facebook, and the approach demonstrably reduces allocations and runtime.
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chapters (6)
- 0:00Introduction to persistence
- 1:36The problem with mutability
- 3:46Immutability and copying
- 5:01Understanding persistence
- 6:42Tree-based structural sharing
- 9:31Implementation and resources
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