Either<L, R> class abstract

A generic type that represents a value of one of two possible types (a disjoint union).

Instances of Either are either an instance of Left or Right.

  • Left is used to represent failure, typically holding an error or exception.
  • Right is used to represent success, typically holding a valid result.

Either<L, R> is commonly used as a functional alternative to throwing exceptions.

Example:

void main() {
  final result1 = divide(10, 2);
  final result2 = divide(5, 0);

  result1.fold(
    (error) => print('Error: $error'),
    (value) => print('Result: $value'),
  ); // Prints: Result: 5

  result2.fold(
    (error) => print('Error: $error'),
    (value) => print('Result: $value'),
  ); // Prints: Error: Cannot divide by zero

  // Using map
  final mappedResult = result1.map((value) => value * 2);
  print(mappedResult.getRight()); // Prints: 10
}

Either<String, int> divide(int a, int b) {
  if (b == 0) {
    return const Left('Cannot divide by zero');
  } else {
    return Right(a ~/ b);
  }
}
Implementers

Constructors

Either()
Creates an Either instance.
const

Properties

hashCode → int
The hash code for this object.
no setterinherited
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited

Methods

flatMap<R2>(Either<L, R2> f(R right)) → Either<L, R2>
Applies the function f to the value contained in Right, if it exists, and returns a new Either containing the result. If this is a Left, it is returned unchanged.
fold<B>(B ifLeft(L left), B ifRight(R right)) → B
Applies one of two functions depending on whether this is a Left or Right.
getLeft() → L
Returns the Left value if this is a Left, otherwise throws.
getRight() → R
Returns the Right value if this is a Right, otherwise throws.
isLeft() → bool
Returns true if this is a Left.
isRight() → bool
Returns true if this is a Right.
map<R2>(R2 f(R right)) → Either<L, R2>
Transforms the value contained in Right using the given function f, returning a new Either with the transformed value.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
toString() → String
A string representation of this object.
inherited

Operators

operator ==(Object other) → bool
The equality operator.
inherited