ruxo / foundation

Foundation library

RZ Functional library for C#

This library is an add-on to LanguageExt library. It tries to provide some syntactic sugar for more natural expression.

Option[T] Extension (RZ.Foundation)

Convert between C# nullable value and Option[T]

Prelude module provides conversion functions for C# nullable and Option[T]. Unfortunately, Value Type/Ref Type semantic differences make creating generic functions to support both meta-types tedious and, in some case, confuse the compiler and generating a warning.

using static LanguageExt.Prelude;

int? x = 123;
Option<T> y = Some(x);  // convert a nullable value to Option<T>
int? z = y.ToNullable(); // convert an Option<T> to a nullable value

// this should also work with nullable ref value
string? a = "Hello";
Option<string> b = Some(a);
string? c = b.ToNullable();

Getting a value out of Option[T]

Suppose that we have follow option values:

using static LanguageExt.Prelude;

var some = Some(123);
var none = Option<int>.None;

Get

var x = some.Get();     // 123
var y = none.Get();     // an exception is thrown!

GetOrThrow

In case you want to specific an exception.

var x = some.GetOrThrow(() => new MyException());     // 123
var y = none.GetOrThrow(() => new MyException());     // MyException is thrown!

GetOrDefault

var x = some.GetOrDefault();   // 123
var y = none.GetOrDefault();   // 0, int's default value

Replace None value

using static LanguageExt.Prelude;
var x = Option<int>.None;
var y = x.OrElse(123);  // Option<int> of 123
var z = x.OrElse(Some(456)) // Option<int> of 456
var a = x.OrElse(() => None);    // stay None
var b = await x.OrElseAsync(() => Task.FromResult(999));    // Option<int> of 999

Perform action (Side effect)

Then is the operation to perform an action. The method returns the original value.

using static LanguageExt.Prelude;
var x = None<int>();
x.Then(v => Console.WriteLine("Value = {0}", v));
x.Then(v => Console.WriteLine("Value = {0}", v), () => Console.WriteLine("No value"));

// async versions
await x.ThenAsync(v => Task.Run(() => Console.WriteLine("V = {0}", v)));
await x.ThenAsync(v => Task.Run(() => Console.WriteLine("V = {0}", v)),
                  () => Task.Run(() => Console.WriteLine("No value")));

Type casting

Option<object> x = Some((object) "I am string");
Option<string> y = x.TryCast<object,string>();
Option<int> z = x.TryCast<object,int>();   // None!

TaskOption[T]

LanguageExt's OptionAsync should be a wrapper of Task<Option<T>>, but its recent async/await handler has been implemented in way that consumes all exceptions as None value. This makes sense when we don’t want any side-effect. But in case of exception handling, I find that by allowing exceptions as the side-effect, would simplify error handling code when writing in functional paradigm.

So TaskOption<T> is made to work similar to OptionAsync but with async/await pattern that allows exceptions to be escalated normally, as well as, support None returning value.