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Description:

result monad

A Dart implementation of the Result Monad found in Rust and other languages.
This models either success (ok) or failure (error) of operations to allow for
more expressive result generation and processing without using exceptions.
This blog post
I wrote goes into the backgrounds of Result Monads and steps through the
various aspects of the implementation for this library.
Features #

Result Monad with standard ok and error constructors
Methods/properties for directly querying if it is encapsulating a success
or failure result and to get those values
runCatching and runCatchingAsync to encapsulate thrown exception objects into error Results
getValueOrElse and getErrorOrElse methods to return a default value if
it is not the respective desired monad
andThen, transform, andThenAsync, transformAsync for chaining together
operations with short-circuit capability
withResult and withResultAsync for processing results in a pass-through capability with
short-circuiting on thrown exceptions
withError and withErrorAsync for processing errors in a pass-through capability with
short-circuiting on thrown exceptions
mapValue, mapError, errorCast methods for transforming success and failure types
match method for performing different operations on a success or failure
monad
fold method for transforming the monad into a new result type with different
logic for

Getting started #
In the pubspec.yaml of your Dart/Flutter project, add the following dependency:
dependencies:
result_monad: ^2.3.2
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In your source code add the following import:
import 'package:result_monad/result_monad.dart';
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Usage #
Below is a simple example but see the repository for feature rich versions:
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));
}
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Additional information #
This result monad implementation takes inspiration from the
Rust result type
and the Kotlin Result
implementation of the Result Monad.
The pub.dev package page can be found here.