when<C> method

C when<C>({ required C ifLeft(Left<L, R> left), required C ifRight(Right<L, R> right), })

Applies ifLeft if this is a Left or ifRight if this is a Right. Since Dart 3.0.0, you can use "switch expression" instead of this method.

This is quite similar to fold, but with fold, arguments will be called with Right.value or Left.value, while the arguments of when will be called with Right or Left itself.

ifLeft is the function to apply if this is a Left. ifRight is the function to apply if this is a Right. Returns the results of applying the function.

Example

final Either<String, int> result = Right(1);

// Prints operation succeeded with 1
result.when(
  ifLeft: (left) => print('operation failed with ${left.value}') ,
  ifRight: (right) => print('operation succeeded with ${right.value}'),
);

Implementation

C when<C>({
  required C Function(Left<L, R> left) ifLeft,
  required C Function(Right<L, R> right) ifRight,
}) {
  final self = this;
  return switch (self) { Left() => ifLeft(self), Right() => ifRight(self) };
}