vibe-types:scala

Scala 3 — Compile-Time Safety Techniques

Base path: ${CLAUDE_PLUGIN_ROOT}/skills/scala3

Full catalog (type system features → constraints they enforce)

• Union & intersection types — express alternatives without common supertype (A | B); combine capabilities (A & B) → catalog/T02-union-intersection.md

• Type lambdas — abstract over type constructors inline; partially apply binary constructors for type-class shapes → catalog/T40-type-lambdas.md

• Match types — compute types from types via pattern matching; type-level conditional logic → catalog/T41-match-types.md

• Givens & using clauses — principled type-class dispatch; compiler supplies evidence automatically → catalog/T05-type-classes.md

• Context functions & context bounds — abstract over contextual dependencies as types; lightweight capability annotation → catalog/T42-context-functions.md

• Extension methods — attach operations to types you don't own; conditional syntax via type-class evidence → catalog/T19-extension-methods.md

• Type-class derivation — auto-generate instances for any ADT from compile-time structure → catalog/T06-derivation.md

• Multiversal equality — restrict == so only semantically meaningful comparisons compile → catalog/T20-equality-safety.md

• Conversions, by-name params, deferred givens — explicit opt-in conversions; break circular given dependencies → catalog/T18-conversions-coercions.md

• Enums, ADTs, GADTs — closed variant sets with exhaustive matching; per-branch type refinement → catalog/T01-algebraic-data-types.md

• Opaque types — zero-cost distinct types sharing same representation; prevent value mix-ups without boxing → catalog/T03-newtypes-opaque.md

• open, export, transparent — control extensibility; delegate via composition; suppress traits from inferred types → catalog/T21-encapsulation.md

• Matchable & TypeTest — prevent pattern matching from breaking type abstractions; sound runtime type tests → catalog/T14-type-narrowing.md

• Structural & refined types, named tuples — statically-checked duck typing; lightweight records without case classes → catalog/T07-structural-typing.md

• Kind polymorphism — type parameters ranging over any kind; universal type tags → catalog/T35-universes-kinds.md

• Inline & compile-time ops — constant folding, dead-branch elimination, compile-time specialization → catalog/T16-compile-time-ops.md

• Macros (quotes & splices) — type-safe compile-time code generation and AST transformation → catalog/T17-macros-metaprogramming.md

• Explicit nulls — reference types never hold null unless explicitly T | Null → catalog/T13-null-safety.md

• Erased definitions — compile-time-only parameters; zero-cost type-level evidence → catalog/T27-erased-phantom.md

• Capture checking & CanThrow — track captured capabilities; effect tracking and purity enforcement at type level → catalog/T12-effect-tracking.md

• Experimental: named type args, into, modularity — selective type parameter binding; fine-grained conversion control → catalog/T43-experimental-preview.md

• Changed & dropped features — more predictable inference and resolution; removed unsound Scala 2 features → catalog/T44-changed-dropped.md

• Refinement types — value-level predicates enforced at compile time via Iron or refined libraries → catalog/T26-refinement-types.md

• Generics & bounded polymorphism — upper/lower bounds, context bounds, F-bounded polymorphism → catalog/T04-generics-bounds.md

• Variance & subtyping — covariant +A, contravariant -A, invariant; Liskov at the type level → catalog/T08-variance-subtyping.md

• Callable types & overloading — function types, SAM types, eta-expansion, method overloading → catalog/T22-callable-typing.md

• Type aliases — transparent aliases, parameterized aliases, type members, path-dependent types → catalog/T23-type-aliases.md

• Record types & data modeling — case classes, named tuples, product types with auto-derived methods → catalog/T31-record-types.md

• Self types — self-type annotations (self: T =>), capability requirements without inheritance → catalog/T33-self-type.md

• Nothing & bottom type — universal subtype, throw, ???, empty collections, covariant widening → catalog/T34-never-bottom.md

• Singleton types & compile-time value parameters — literal types, constValue, compiletime.ops; encode sizes/dimensions in types → catalog/T15-const-generics.md

• Literal types — every literal has a singleton type; foundation for type-level computation and value discrimination → catalog/T52-literal-types.md

• Path-dependent types — type members, instance-dependent types (x.Inner), abstract type members → catalog/T53-path-dependent-types.md

• Immutability markers — val, final, sealed, immutable collections; immutability is the default → catalog/T32-immutability-markers.md

• Trait-based dynamic dispatch — traits + abstract classes for runtime polymorphism; JVM vtable → catalog/T36-trait-objects.md

• Given/implicit resolution — Scala's trait solver: search scopes, priority, divergence detection → catalog/T37-trait-solver.md

• Associated types — abstract type members in traits; alternative to type parameters → catalog/T49-associated-types.md

• Annotations & compiler directives — @inline, @tailrec, @targetName, @deprecated → catalog/T39-notation-attributes.md

• Dependent types (via path-dependent + match types) — approximate value-indexed patterns → catalog/T09-dependent-types.md

• Coherence & instance scoping (via given import rules) — no orphan rule; import-based visibility → catalog/T25-coherence-orphan.md

• Functor / Applicative / Monad — map, flatMap, pure; compositional effect chaining via cats → catalog/T54-functor-applicative-monad.md

• Monad transformers — EitherT, StateT, ReaderT; compose effects in a stack → catalog/T55-monad-transformers.md

• Tagless final — decouple program description from interpretation; swap runtimes → catalog/T56-tagless-final.md

• Typestate pattern — phantom types track state; invalid transitions don't compile → catalog/T57-typestate.md

• Witness & evidence types — =:=, <:<, given evidence; compiler proves preconditions → catalog/T58-witness-evidence.md

• Existential types — abstract type members, wildcard types; hide concrete types → catalog/T59-existential-types.md

• Recursive types — sealed enum/trait hierarchies defined in terms of themselves → catalog/T61-recursive-types.md

Use cases (problem → which features help)

• Preventing invalid states — make impossible states impossible via ADTs, opaque types, phantom types, GADTs → usecases/UC01-invalid-states.md
• Domain modeling — newtypes, smart constructors, closed state hierarchies, capability composition → usecases/UC02-domain-modeling.md
• Access & encapsulation — hide representations, selective delegation, controlled inheritance, scope qualifiers → usecases/UC10-encapsulation.md
• Effect tracking — checked exceptions, capability passing, Reader/Writer patterns, tagless final → usecases/UC11-effect-tracking.md
• Compile-time programming — inline branching, type-level arithmetic, macros for validation and codegen → usecases/UC12-compile-time.md
• Protocol & state machines — enforce valid call ordering at compile time; phantom builders, GADT protocols → usecases/UC13-state-machines.md
• Extensibility — type-class pattern, extension methods, export for delegation, open modifier → usecases/UC14-extensibility.md
• Equality & comparison — prevent nonsensical equality checks; multiversal equality, CanEqual derivation → usecases/UC15-equality.md
• Nullability & optionality — eliminate NPEs through explicit nulls, union types, match types → usecases/UC16-nullability.md
• Variance & subtyping — control covariance/contravariance precisely; opaque types breaking subtyping → usecases/UC17-variance.md
• Type-level arithmetic — enforce numeric constraints at compile time; compiletime.ops, match type recursion → usecases/UC18-type-arithmetic.md
• Serialization codecs — auto-derive serializers with full type safety; Mirror inspection, schema validation → usecases/UC19-serialization.md
• DSL & builder patterns — type-safe DSLs where invalid compositions are compile errors; context functions, phantom builders → usecases/UC09-builder-config.md
• Error handling — CanThrow capabilities, error ADTs, union type channels → usecases/UC08-error-handling.md