ErrorOr.Extensions 1.2.0

ErrorOr.Extensions

An extension library for ErrorOr by Amichai Mantinband.

Features

This library extends the ErrorOr library with useful features to allow for some specific workflows, for creating meaningful error handling in your applications.

Select and SelectMany

An instance of an ErrorOr<T> can be seen as a list containing a single element or none. With that in mind it would be useful you have the ability to map an ErrorOr<T> to a new type/value. This library provides two extensions to allow for this: Select and SelectMany.

The method signatures look basically the same as for IEnumarable<T>:

ErrorOr<TResult> Select<T, TResult>(this ErrorOr<T> errorOr, Func<T, TResult> mapping)

ErrorOr<TResult> SelectMany<T, TResult>(this ErrorOr<T> errorOr, Func<T, ErrorOr<TResult>> mapping)

These methods allow for changing the value inside an ErrorOr<T> if it is successful, but keep the errors intact if it is erroneous.

Example:

ErrorOr<string> errorOr = ErrorOrFactory.From(42).Select(value => value.ToString());

ErrorOr<string> errorOr = ErrorOrFactory.From(42).SelectMany(value => Mapping(value));
ErrorOr<string> Mapping(int value) => ErrorOrFactory.From(value.ToString());

Async

Many APIs work asynchronous with Task<T> as return type. When using such APIs that return Task<ErrorOr<T>> it is useful to be able to use Select and SelectMany on them as well without having to strip the Task<T> beforehand.

This library has you covered. Both, Select and SelectMany are provided in three variants:

Task<ErrorOr<TResult>> Select<T, TResult>(this ErrorOr<T> errorOr, Func<T, Task<TResult>> mapping)
Task<ErrorOr<TResult>> Select<T, TResult>(this Task<ErrorOr<T>> errorOrTask, Func<T, TResult> mapping)
Task<ErrorOr<TResult>> Select<T, TResult>(this Task<ErrorOr<T>> errorOrTask, Func<T, Task<TResult>> mapping)
Task<ErrorOr<TResult>> SelectMany<T, TResult>(this ErrorOr<T> errorOr, Func<T, Task<ErrorOr<TResult>>> mapping)
Task<ErrorOr<TResult>> SelectMany<T, TResult>(this Task<ErrorOr<T>> errorOrTask, Func<T, ErrorOr<TResult>> mapping)
Task<ErrorOr<TResult>> SelectMany<T, TResult>(this Task<ErrorOr<T>> errorOrTask, Func<T, Task<ErrorOr<TResult>>> mapping)

Every use case should be covered.

LINQ and LINQ async

This library provides LINQ extensions for ErrorOr. This enables a very clean approach of binding multiple ErrorOr generating function together. You can write them with the usual from x in y select x syntax you know and love from LINQ. If an error occurs along the way, processing the chain is interrupted and the collected errors are passed to the resulting instance of ErrorOr<T>.

Example:

ErrorOr<string> errorOr =
    from userId in ParseInput("10")            // returns ErrorOr<int>
    from user in userRepository.Lookup(userId) // returns ErrorOr<User>
    select user.Name                           // maps to string

This also works if the methods that are chained are asynchronous:

Task<ErrorOr<string>> errorOr =
    from userId in ParseInput("10")            // returns Task<ErrorOr<int>>
    from user in userRepository.Lookup(userId) // returns Task<ErrorOr<User>>
    select user.Name                           // maps to string

Closing

The author of this extension library is not affiliated with Amichai Mantinband nor does he claim anything from the ErrorOr library.