dart_either 2.1.0

Either monad for Dart language and Flutter framework. Type-safe error handling, railway oriented programming. Supports Monad comprehensions, async map, async flatMap.

2.1.0 Mar 07, 2026

• Promoted Either.parSequenceN and Either.parTraverseN from experimental to stable.
• Added complete API docs and examples for Either.parSequenceN and Either.parTraverseN.
• Added unit tests for Either.parSequenceN and Either.parTraverseN, including concurrency-limit and short-circuit cases.
• Added @useResult annotations to public APIs that should not be ignored (for example: isLeft, isRight, map, flatMap, swap, exists, all, toEitherStream, left, right, and others).

API migration notes

• Either.parSequenceN changed from positional parameters to named parameters:

  // Before (2.0.0)
  Either.parSequenceN<String, int>(functions, n);
  
  // Now (2.1.0)
  Either.parSequenceN<String, int>(
    functions: functions,
    maxConcurrent: n,
  );
  

• Either.parTraverseN changed from positional parameters to named parameters:

  // Before (2.0.0)
  Either.parTraverseN<String, int, int>(values, mapper, n);
  
  // Now (2.1.0)
  Either.parTraverseN<String, int, int>(
    values: values,
    mapper: mapper,
    maxConcurrent: n,
  );
  

• maxConcurrent controls concurrency.
  • Pass a number (for example 2) to limit concurrency.
  • Pass null for unlimited concurrency.

2.0.0 Sep 01, 2024

• Require Dart 3.0.0 or higher >=3.0.0 <4.0.0.

• Make Either a sealed class, EitherEffect a sealed class, and ControlError a final class. Now you can use exhaustive switch expressions on Either instances.

  final Either<String, int> either = Either.right(10);
    
  // Use the `when` method to handle
  either.when(
    ifLeft: (l) => print('Left: $l'),
    ifRight: (r) => print('Right: $r'),
  ); // Prints Right: Either.Right(10)
    
  // Or use Dart 3.0 switch expression syntax 🤘
  print(
    switch (either) {
      Left() => 'Left: $either',
      Right() => 'Right: $either',
    },
  ); // Prints Right: Either.Right(10)
  

1.0.0 Aug 23, 2022

• This is our first stable release.

0.0.1 Apr 27, 2021

• Initial version, created by Stagehand