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);
  }
}

Available extensions

Constructors

Either(): Creates an Either instance.
const

Properties

errorOrNull → E?: Available on Either<E, T>, provided by the GmanaValueObjectResultX extension
The validation error, or null when validation succeeded.
no setter
hashCode → int: The hash code for this object.
no setterinherited
isInvalid → bool: Available on ValidationResult<TIssue, TValue>, provided by the GmanaValidationResultX extension
Whether validation failed.
no setter
isInvalid → bool: Available on Either<E, T>, provided by the GmanaValueObjectResultX extension
Whether validation failed.
no setter
issueOrNull → TIssue?: Available on ValidationResult<TIssue, TValue>, provided by the GmanaValidationResultX extension
The typed validation issue, or null when validation succeeded.
no setter
isValid → bool: Available on ValidationResult<TIssue, TValue>, provided by the GmanaValidationResultX extension
Whether validation succeeded.
no setter
isValid → bool: Available on Either<E, T>, provided by the GmanaValueObjectResultX extension
Whether validation succeeded.
no setter
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited
valueOrNull → TValue?: Available on ValidationResult<TIssue, TValue>, provided by the GmanaValidationResultX extension
The validated value, or null when validation failed.
no setter
valueOrNull → T?: Available on Either<E, T>, provided by the GmanaValueObjectResultX extension
The validated value, or null when validation failed.
no setter

Methods

all(bool test(R right)) → bool: Returns true when this is a Left or when test passes for the Right value.
bimap<L2, R2>(L2 ifLeft(L left), R2 ifRight(R right)) → Either<L2, R2>: Applies ifLeft or ifRight and returns a new Either with mapped values.
contains(R value) → bool: Returns true when this is a Right containing value.
exists(bool test(R right)) → bool: Returns true when this is a Right and test passes.
filterOrElse(bool test(R right), L onFalse(R right)) → Either<L, R>: Demotes a Right to a Left when test fails.
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.
flatMapAsync<R2>(FutureOr<Either<L, R2>> f(R right)) → Future<Either<L, R2>>: Asynchronously applies f to the Right value, if present.
flatMapLeft<L2>(Either<L2, R> f(L left)) → Either<L2, R>: Chains on the Left side — the mirror of flatMap.
fold(B ifLeft(L left), B ifRight(R right)) → B: Applies one of two functions depending on whether this is a Left or Right.
foldAsync(FutureOr ifLeft(L left), FutureOr ifRight(R right)) → Future: Asynchronously applies one of two functions depending on the side present.
getLeft() → L: Returns the Left value if this is a Left, otherwise throws.
getOrDefault(R defaultValue) → R: Returns the Right value, or defaultValue when this is a Left.
getOrElse(R orElse(L left)) → R: Returns the Right value if this is a Right, otherwise computes a fallback.
getOrNull() → R?: Returns the Right value if this is a Right, otherwise null.
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.
leftOrNull() → L?: Returns the Left value if this is a Left, otherwise null.
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.
mapAsync<R2>(FutureOr<R2> f(R right)) → Future<Either<L, R2>>: Asynchronously transforms the Right value using f, if present.
mapLeft<L2>(L2 f(L left)) → Either<L2, R>: Maps the Left value using f, if present.
messageOrNull([ValidationErrorMessages messages = const DefaultValidationErrorMessages()]) → String?: Available on Either<E, T>, provided by the GmanaValueObjectResultX extension
Resolves the validation error to a message, or returns null on success.
messageOrNull(ValidationMessageResolver<TIssue> resolve) → String?: Available on ValidationResult<TIssue, TValue>, provided by the GmanaValidationResultX extension
Resolves the validation issue to a message, or returns null on success.
noSuchMethod(Invocation invocation) → dynamic: Invoked when a nonexistent method or property is accessed.
inherited
orElse(Either<L, R> f(L left)) → Either<L, R>: Returns this Either when it is a Right, otherwise the result of f.
orElseWith<L2>(Either<L2, R> f(L left)) → Either<L2, R>: Like orElse but the recovery may produce a different Left type.
recover(R f(L left)) → Either<L, R>: Turns a Left into a Right by computing a fallback value.
rightOrNull() → R?: Returns the Right value if this is a Right, otherwise null.
swap() → Either<R, L>: Swaps the sides of this Either, turning Left into Right and vice versa.
tap(void f(R right)) → Either<L, R>: Runs f with the Right value, if present, and returns this Either.
tapLeft(void f(L left)) → Either<L, R>: Runs f with the Left value, if present, and returns this Either.
toEmailDomainResult() → Either<EmailError, Email>: Available on Either<EmailValidationIssue, String>, provided by the EmailValidationAdapterX extension
Converts this validation result to a domain Email result with EmailError.
toEmailValueObject() → Either<EmailValidationIssue, Email>: Available on Either<EmailValidationIssue, String>, provided by the EmailValidationAdapterX extension
Converts a successful validation into an Email value object.
toIdentifierDomainResult() → Either<IdentifierError, IdentifierValue>: Available on Either<IdentifierValidationIssue, String>, provided by the IdentifierValidationAdapterX extension
Converts this validation result to a domain IdentifierValue result with IdentifierError.
toIdentifierValueObject() → Either<IdentifierValidationIssue, IdentifierValue>: Available on Either<IdentifierValidationIssue, String>, provided by the IdentifierValidationAdapterX extension
Converts a successful validation into an IdentifierValue value object.
toList() → List<R>: A single-element list for a Right, or an empty list for a Left.
toNetworkAddressDomainResult() → Either<NetworkAddressError, NetworkAddressValue>: Available on Either<NetworkValidationIssue, String>, provided by the NetworkValidationAdapterX extension
Converts this validation result to a domain NetworkAddressValue result with NetworkAddressError.
toNetworkAddressValueObject() → Either<NetworkValidationIssue, NetworkAddressValue>: Available on Either<NetworkValidationIssue, String>, provided by the NetworkValidationAdapterX extension
Converts a successful validation into a NetworkAddressValue value object.
toNumberDomainResult() → Either<NumberError, NumberValue>: Available on Either<NumberValidationIssue, num>, provided by the NumberValidationAdapterX extension
Converts this validation result to a domain NumberValue result with NumberError.
toNumberValueObject() → Either<NumberValidationIssue, NumberValue>: Available on Either<NumberValidationIssue, num>, provided by the NumberValidationAdapterX extension
Converts a successful validation into a NumberValue value object.
toOption() → Option<R>: Discards the Left value, keeping only whether a Right was present.
toPasswordDomainResult() → Either<PasswordError, Password>: Available on Either<PasswordValidationIssue, String>, provided by the PasswordValidationAdapterX extension
Converts this validation result to a domain Password result with PasswordError.
toPasswordValueObject() → Either<PasswordValidationIssue, Password>: Available on Either<PasswordValidationIssue, String>, provided by the PasswordValidationAdapterX extension
Converts a successful validation into a Password value object.
toPhoneDomainResult() → Either<PhoneError, PhoneValue>: Available on Either<PhoneValidationIssue, String>, provided by the PhoneValidationAdapterX extension
Converts this validation result to a domain PhoneValue result with PhoneError.
toPhoneValueObject() → Either<PhoneValidationIssue, PhoneValue>: Available on Either<PhoneValidationIssue, String>, provided by the PhoneValidationAdapterX extension
Converts a successful validation into a PhoneValue value object.
toResult() → GResult<R, L>: Available on Either<L, R>, provided by the GmanaEitherToResultX extension
Converts this Either to a GResult, mapping Left to GFailure and Right to GSuccess.
toString() → String: A string representation of this object.
inherited
toTextDomainResult() → Either<TextError, TextValue>: Available on Either<TextValidationIssue, String>, provided by the TextValidationAdapterX extension
Converts this validation result to a domain TextValue result with TextError.
toTextValueObject() → Either<TextValidationIssue, TextValue>: Available on Either<TextValidationIssue, String>, provided by the TextValidationAdapterX extension
Converts a successful validation into a TextValue value object.
toUrlDomainResult() → Either<UrlError, UrlValue>: Available on Either<UrlValidationIssue, Uri>, provided by the UrlValidationAdapterX extension
Converts this validation result to a domain UrlValue result with UrlError.
toUrlValueObject() → Either<UrlValidationIssue, UrlValue>: Available on Either<UrlValidationIssue, Uri>, provided by the UrlValidationAdapterX extension
Converts a successful validation into an UrlValue value object.
zip<R2>(Either<L, R2> other) → Either<L, (R, R2)>: Pairs the Right values of this and other.
zipWith<R2, R3>(Either<L, R2> other, R3 combine(R first, R2 second)) → Either<L, R3>: Combines the Right values of this and other through combine.

Operators

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

Static Methods

cond<L, R>(bool test, L ifFalse(), R ifTrue()) → Either<L, R>: Builds a Right from ifTrue when test holds, otherwise a Left from ifFalse.
fromNullable<L, R>(R? value, L onNull()) → Either<L, R>: Lifts a nullable value into an Either, using onNull for the Left side.
sequence<L, R>(Iterable<Either<L, R>> items) → Either<L, List<R>>: Collapses items into a single Either holding every Right value.
traverse<L, R, R2>(Iterable<R> items, Either<L, R2> f(R item)) → Either<L, List<R2>>: Applies f to every element of items and sequences the results.
tryCatch<L, R>(R fn(), L onError(Object error, StackTrace stackTrace)) → Either<L, R>: Executes fn and catches any exception, returning Right on success or Left(onError(error, stackTrace)) on failure.
tryCatchAsync<L, R>(FutureOr<R> fn(), L onError(Object error, StackTrace stackTrace)) → Future<Either<L, R>>: Asynchronously executes fn and catches any exception, returning Right on success or Left(onError(error, stackTrace)) on failure.