Added #

• New sealed Twofold<S, E> core type with explicit Success and Error states
• Factory constructors:
  • Twofold.success
  • Twofold.error
• Unified when API for both side effects and value transformation
• Safe accessors:
  • successOrNull
  • errorOrNull
• Explicit unsafe accessors:
  • successUnsafe
  • errorUnsafe
• Transformation helpers:
  • mapSuccess
  • mapError
• Chaining helper:
  • flatMapSuccess
• Fallback helpers:
  • getOrElse
  • getOrElseGet
• Utility helper:
  • swap

Async #

• Added async extensions for Future<Twofold>:
  • mapSuccess
  • mapError
  • flatMapSuccess
  • when
  • getOrElse
  • getOrElseGet
  • swap
• Added async factory helpers via TwofoldFuture:
  • fromCondition
  • tryCatch

Testing #

• Added framework-agnostic testing helpers:
  • expectSuccess
  • expectError

Documentation #

• Rewritten README to match sealed-class API
• Added comprehensive Dartdoc examples for all public APIs
• Added CONTRIBUTING.md defining design rules, naming conventions, and stability guarantees

Changed #

• Replaced record-based left/right representation with sealed classes
• Replaced fold API with unified when
• Standardized terminology to Success / Error
• Improved equality and hashing guarantees using value-based semantics

Removed #

• Removed record-based Twofold<L, R> implementation
• Removed left, right, isLeft, isRight, mapLeft, and legacy helpers
• Removed possibility of invalid states (now enforced by design)

Notes #

• This release contains intentional breaking changes from 0.1.0
• The API surface is now stable and designed for evolution toward 1.0.0
• Users upgrading from 0.1.0 should refer to the README for migration guidance

Added #

• Record-based Twofold<L, R> core type for representing two-outcome values
• Constructors for creating left and right values
• Extension methods for:
  • inspecting state (isLeft, isRight)
  • safe and unsafe value access
  • handling outcomes (fold, when)
  • transforming values (map, mapLeft, flatMap)
  • fallback handling (getOrElse, getOrElseGet)
  • utility helpers (swap, toList, toStringValue, isEqualTo, hashValue)

Notes #

• Invalid states (both values null) were possible and would throw at runtime
• API was synchronous and minimal by design