RResult 0.2.0

RResult

A Result type for modelling 2way pipeline for C Sharp.

Introduction

The Result type is a monad type that holds return values and errors. By holding the state after an operation, such as a function, in the Result type, the result of the execution can be clearly defined. If an element T is found, the successful value can be retrieved from Ok<T>, and if an error is found, the failed result can be retrieved from Err<E>. This avoids ambiguity in the handling of possible value absences such as null, or complications in the processing path due to exception throws.

The Result type of this project is represented as type RResult. The initials R are derived from Rust and Railway Oriented Programming.

Gettings Started

dotnet add package RResult

This is a FizzBuzz with Result type. It can be described in a declarative, flow-controlled, natural language alike, showing that it can be coded simply and robustly. Full sample is ./example/RResult.FizzBuzz

    static void Main(string[] args) =>
        Console.WriteLine(
            string.Join(",", Enumerable.Range(1, 30).Select(Pipeline))
        );

    static string Pipeline(int i) =>
        DoDivide(i, 15, "FizzBuzz")
            .OrElse(it => DoDivide(it, 3, "Fizz"))
            .OrElse(it => DoDivide(it, 5, "Buzz"))
            .MapBoth(
                Ok => $"{Ok}",
                Err => $"{Err}"
            );

    static RResult<string, int> DoDivide(int dividend, int divisor, string sig) =>
        (dividend % divisor) switch
        {
            0 => sig,
            _ => dividend,
        };

Transforming Results

Both success/error values can be converted through Map / MapErr.

RResult<int, SomeErr>.Ok(3) // Ok(3)
    .Map(a => a * a) // Ok(9))
    // Also you can convert type int to string
    .Map(n => $"{n}") // OK("9")

Mehod Chain

Results can be chain.

Async Task Function

Also some functions are support AsyncFunction. Will be fully compliant in the future.

• MapAsync / MapErrAsync
• InspectAsync / InspectErrAsync
• AndThenAsync / AndThenErrAsync

Combine Result

Not currently supported, but will be in the future

Inspiration

Inspiration for this library has been drawn:

• Rust
• kotlin-result

Improvements on existing solutions

• Feature parity with Result types from other languages including Rust
• Lax constraints on success value nullability
• Consistent naming with existing Result libraries from other languages (e.g. map, mapError, mapBoth, and, andThen, or, orElse, unwrap)
• Unit tests covering every library method

Comparison table with other projects

Contributing

Bug reports and pull requests are welcome on [GitHub][github].

License

This project is available under the terms of the Apache ver 2.0 license. See the LICENSE file for the copyright information and licensing terms.