result_monad 1.0.1

A Dart implementation of the Result Monad which allows for more expressive result generation and processing without using exceptions.

example/example.md

Examples

The project ships with examples which you can find here.

Simple Usage

The simplest usage begins with defining the function return to be a Result Monad. The monad takes two types, the value type for when it succeeds and an error type for if it fails. The value type is always whatever the natural return of the function would be. The error type can be literally anything. For more complex cases you may have a reusable object type. For cases where you use the runCatching method to wrap exception-generating code in a way that returns a Result monad it'll be whatever the Exception type that was thrown. In the below case it is simply an error String. Since the monad can be queried for if it is encapsulating a success isSuccess or failed isFailure options the type chosen is more for how the developer decides to propagate their errors.

In the below case we aren't directly querying it but instead using the match method to have two different code paths depending on whether we are dealing with a succeeded or failed result. See the API documentation for more details.

import 'package:result_monad/result_monad.dart';

Result<double, String> invert(double value) {
  if (value == 0) {
    return Result.error('Cannot invert zero');
  }

  return Result.ok(1.0/value);
}

void main() {
  // Prints 'Inverse is: 0.5'
  invert(2).match(
      onSuccess: (value) => print("Inverse is: $value"),
      onError: (error) => print(error));

  // Prints 'Cannot invert zero'
  invert(0).match(
      onSuccess: (value) => print("Inverse is: $value"),
      onError: (error) => print(error));
}```