Optional.Async

Async extensions for Nils Luck's Optional library.

It allows you to chain Task<Option<T>> and Task<Option<T, TException>> without having to use await.

Since version 5.0, the Optional library will include its own async extensions. However, at this point they don't provide as much flexibility. To avoid conflicts, the namespace of this library has been changed to Optional.Async.Extensions.

Note: Optional.Async was not meant to be published as a standalone library. It's a collection of extension methods that I had to implement on my own while working with Optional. There are currently no tests and I don't plan on extensively maintaining it. Still, most of the extensions you'll find here are currently being used/have been used for the past year in production code without issues.

Usage

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Say you have the following asynchronous functions and you want to execute them in order:

Task<Option<User, Error>> CheckIfUserIsAuthorized(string userId, string category);

Task<Option<CloudRecord, Error>> StoreTheFileIntoTheCloud(File file, string category);

Task<Option<Guid, Error>> StoreDatabaseLog(CloudRecord record);

Task<Option<DocumentProcessedResult, Error>> SendToExternalService(Guid key);

Currently, there is no built-in mechanism inside Optional that allows you to chain these calls. What Optional.Async provides is the ability to compose asynchronous functions. The following would be valid syntax:

Task<Option<DocumentProcessedResult, Error>> ProcessDocument(
    string userId,
    string category,
    File file) =>
    CheckIfUserIsAuthorized(userId, category).FlatMapAsync(user =>
    StoreTheFileIntoTheCloud(file, category).FlatMapAsync(cloudRecord =>
    StoreDatabaseLog(cloudRecord).FlatMapAsync(uniqueKey =>
    SendToExternalService(uniqueKey))));

See the DevAdventures RealWorld project and the DDD Café for more examples.

How to install

It's available as a NuGet package under Optional.Async.