A multiplatform Result monad for modelling success or failure operations.

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kotlin-result

Result<V, E> is a monad for modelling success (Ok) or failure (Err) operations.

Inspiration

Inspiration for this library has been drawn from other languages in which the Result monad is present, including:

It also iterates on other Result libraries written in Kotlin, namely:

Improvements on the existing solutions include:

Feature parity with Result types from other languages including Elm, Haskell, & Rust
Multiplatform project support
Lax constraints on value/error nullability
Lax constraints on the error type's inheritance (does not inherit from Exception)
Top level Ok and Err classes avoids qualifying usages with Result.Ok/Result.Err respectively
Higher-order functions marked with the inline keyword for reduced runtime overhead
Extension functions on Iterable & List for folding, combining, partitioning
Consistent naming with existing Result libraries from other languages (e.g. map, mapError, mapBoth, mapEither, and, andThen, or, orElse, unwrap)
Extensive test suite with over 50 unit tests covering every library method

repositories {
    maven { url "https://jitpack.io" }
}

dependencies {
    compile 'com.github.michaelbull:kotlin-result:1.0.5'
}

The unit tests are a good source of examples for using the library as they cover every available method.

Mappings from common Result libraries are available on the wiki:

Bug reports and pull requests are welcome on GitHub.

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