HOW TO EXTEND MAP? ... OR WHY WE NEED COLLECTIONS REDESIGN?
summary
Extending Scala's Map to a Grid (Map[(Int,Int),V] with row) breaks in practice because covariance and builders change return types: filter/map/flatMap use the collection builder so they return Map, not Grid. Fixes require implementing MapLike with adjusted type parameters, providing an implicit CanBuildFrom, and reimplementing withDefault variants; a subtle bug leaves empty inner maps (a memory leak). Practical advice is to prefer composition and minimal overrides rather than inheriting the full collections hierarchy.
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chapters (15)
- 0:00Introduction
- 0:46The problem
- 2:29The collections
- 4:11Immutable map
- 6:49Interface
- 7:35Methods
- 11:07Code
- 12:12Testing
- 13:30Filter method
- 15:34Map method
- 18:17With default
- 19:17Recap
- 20:52Goals for new implementations
- 23:52Memory leak
- 26:39References
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