TYPECLASSES — A TYPE SYSTEM CONSTRUCT
summary
Typeclasses provide ad hoc polymorphism in Scala but are implemented via implicits, which creates surprises: orphan instances roam globally, implicit search picks the most specific available and can cause ambiguity, and overlapping instances break coherence and move-code semantics. Lessons from Haskell and Rust lead to concrete fixes: put instances in companion objects or a dedicated orphan package, use wrapper types for alternative semantics, and use Simulacrum/Cats (macros that generate ops and syntax) to reduce boilerplate and improve discoverability.
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chapters (15)
- 0:00Introduction
- 1:24Supporthoc polymorphism
- 4:08Defining the type class
- 7:50Type class definition
- 12:17Type class implementation
- 12:38Orphan instances
- 14:17Rust
- 16:20Implicit Resolution
- 17:47Issues with Type
- 23:26Simulacrum
- 27:04Cat
- 28:20Orphans
- 28:43OK
- 29:40Maintainability Readability
- 29:59Summary
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