Railway Oriented Programming

Structs

Result

Result object holds the result of an operation or Error It is defined as

public readonly struct Result<TValue>
{
    public TValue Value => IsSuccess ? _value! : throw new InvalidOperationException;
    public Error Error => IsFailure ? _error! : throw new InvalidOperationException;

    public bool IsSuccess => !IsFailure;
    public bool IsFailure { get; }

    public static implicit operator Result<TValue>(TValue value) => Result.Success(value);

    public static implicit operator Result<TValue>(Error error) => Result.Failure<TValue>(error);
 }

Maybe

Maybe object holds a value or nothing. It is defined as

 public readonly struct Maybe<T> :
    IEquatable<T>,
    IEquatable<Maybe<T>>
    where T : notnull
{
   public T Value;
   public bool HasValue;
   public bool HasNoValue;
}

Functions

Bind

Bind calls the given function if the result is in success state and return the new result.

Tap

Tap calls the given function if the result is in success state and returns the same result.

Compensate

Compensate for failed result by calling the given function.

Ensure

Ensure calls the given function if the result is in success state. If the function returns false, the attached error is returned.

Map

Map calls the given function if the result is in success state. The return value is wrapped in Result as success.

Combine

Combine combines multiple Result objects. It will return a Result with all the errors if any of the Result objects have failed. If all the errors are of type ValidationError, then it will return a ValidationError with all the errors. Otherwise it will return an AggregatedError

ParallelAsync

Parallel runs multiple tasks in parallel and returns multiple tasks. AwaitAsync will await all the task and return the combined result.

Finally

Finally unwraps the Result and returns the success value or the error.

Maybe

Maybe states if it contains a value or not. It has the following methods:

• HasValue - returns true if it has a value.
• HasNoValue - returns true if it does not have a value.
• Value - returns the value if it has a value. Otherwise InvalidOperationException