Philiprehberger.OptionType

Option/Maybe monad for explicit null handling with Map, Bind, Match, and LINQ support.

Installation

dotnet add package Philiprehberger.OptionType

Usage

Creating Options

using Philiprehberger.OptionType;

var some = Option.Some(42);
var none = Option.None<int>();
var fromNullable = Option.From<string>(null); // None
var fromValue = Option.From("hello");         // Some("hello")

Transforming Values

var doubled = Option.Some(21).Map(x => x * 2);  // Some(42)

var parsed = Option.Some("123")
    .Bind(s => int.TryParse(s, out var n) ? Option.Some(n) : Option.None<int>());

var positive = Option.Some(42).Filter(x => x > 0);  // Some(42)
var negative = Option.Some(-1).Filter(x => x > 0);  // None

Pattern Matching

string message = Option.Some(42).Match(
    some: v => $"Got {v}",
    none: () => "Nothing"
);

int value = none.ValueOr(0);           // 0
int must = some.ValueOrThrow();        // 42

LINQ Query Syntax

var result = from x in Option.Some(10)
             from y in Option.Some(20)
             select x + y;  // Some(30)

var filtered = from x in Option.Some(42)
               where x > 0
               select x;  // Some(42)

Nullable Conversion

int? nullable = 42;
var option = nullable.ToOption();  // Some(42)

int? nullValue = null;
var noneOption = nullValue.ToOption();  // None

Async Operations

var result = await Option.Some(42)
    .MapAsync(async x => await FetchMultiplierAsync(x));

var bound = await Option.Some("user-123")
    .BindAsync(async id => await FindUserAsync(id));

var message = await Option.Some(42)
    .MatchAsync(
        some: async v => await FormatAsync(v),
        none: () => Task.FromResult("not found")
    );

Fallback with OrElse

var primary = Option.None<int>();
var result = primary.OrElse(Option.Some(99));  // Some(99)

var lazy = primary.OrElse(() => Option.Some(ComputeDefault()));  // factory only called when None

Safe Execution with Try

var parsed = Option.Try(() => int.Parse("42"));         // Some(42)
var failed = Option.Try(() => int.Parse("not a number")); // None

var fetched = await Option.TryAsync(async () => await FetchDataAsync());

Side Effects with Tap

var result = Option.Some(42)
    .Tap(v => Console.WriteLine($"Processing: {v}"))
    .Map(x => x * 2)
    .TapNone(() => Console.WriteLine("No value found"));

API

Option (static)

Method	Description
Some<T>(T value)	Create an Option containing a value
None<T>()	Create an empty Option
From<T>(T? value)	Create an Option from a nullable value
Try<T>(Func<T>)	Wrap a function that may throw into Some or None
TryAsync<T>(Func<Task<T>>)	Wrap an async function that may throw into Some or None

Option<T> (struct)

Member	Description
IsSome	True if the option contains a value
IsNone	True if the option is empty
Map<U>(Func<T, U>)	Transform the contained value
Bind<U>(Func<T, Option<U>>)	Chain option-returning functions
Filter(Func<T, bool>)	Keep value only if predicate holds
Match<U>(Func<T, U>, Func<U>)	Pattern match on the option
MapAsync<U>(Func<T, Task<U>>)	Asynchronously transform the contained value
BindAsync<U>(Func<T, Task<Option<U>>>)	Asynchronously chain option-returning functions
MatchAsync<U>(Func<T, Task<U>>, Func<Task<U>>)	Asynchronously pattern match on the option
OrElse(Option<T>)	Return this option or the fallback
OrElse(Func<Option<T>>)	Return this option or invoke the fallback factory
Tap(Action<T>)	Execute a side effect when Some
TapNone(Action)	Execute a side effect when None
ValueOr(T)	Get value or default
ValueOrThrow()	Get value or throw InvalidOperationException
ToString()	String representation
Equals(Option<T>)	Value equality
GetHashCode()	Hash code

Extension Methods

Method	Description
Select	LINQ select support (maps value)
SelectMany	LINQ multi-from support (binds values)
Where	LINQ where support (filters value)
ToOption()	Convert nullable to Option
Flatten()	Unwrap nested Option<Option<T>>

Development

dotnet build src/Philiprehberger.OptionType.csproj --configuration Release

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License

MIT