when<R> method

R when<R>({ required R success(T result), required R error(Object error, StackTrace? stackTrace), required R inProgress(), required R idle(), })

Provides several callbacks for handling common states of async data. It functions as a rudimentary form of pattern matching.

• idle callback is used to match the initial state where the operation hasn't started yet.
• inProgress is used to handle an ongoing async operation.
• success is called with the finished successful result.
• error is to be called when the operation has finished with an Exception, with an optional StackTrace.

Implementation

R when<R>({
  required R Function(T result) success,
  required R Function(Object error, StackTrace? stackTrace) error,
  required R Function() inProgress,
  required R Function() idle,
}) {
  if (this is _InProgress) {
    return inProgress();
  } else if (this is _Error) {
    final err = this as _Error;
    return error(err.error, err.stackTrace);
  } else if (this is _Success) {
    return success((this as _Success<T>).results);
  } else {
    return idle();
  }
}