Option

What is it?

An Option type for C#. It allows you to clearly distinguish between having a value (Some) and not having a value (None) without using null. This can make your code clearer by flagging whether clients need to handle an empty result. The type also provides a set of powerful operations, providing more flexiblity than using the Try pattern.

Unlike Optional, this library enforces that Option cannot contain null. Instead, null is equivalent to Option.None. As a result, this library supports unambigious implicit casts from T, null and Option.None to Option<T>.

This is a fork of the fantastic Option library, upgraded to netstandard.

How can I get it?

Option is available as a NuGet package: https://www.nuget.org/packages/Option.Netstandard

Example Usage

Create an option with a value

// These are all equivalent
var option = Option.Create(1);
var option = Option.Some(1);
var option = Option<int>.Some(1);
Option<int> option = 1; // Implicit cast from 1 to Option.Some(1)

Create an empty option

// These are all equivalent
int? x = null;
var option = Option.Create(x);
var option = Option<int>.None;
Option<int> option = x;
Option<int> option = Option.None; // Implicit cast from Option.None to Option<int>.None

Terse creation (no need to repeat types)

public Option<string> Match(int x) 
{
  if (x == 1)
    return "one";
  if (x == 2)
    return "two";
  else
    return Option.None;
}

Check for equality

Option.Some(1) == Option.Some(1)  // => True
Option.Some(1) == Option.Some(2)  // => False
Option.Some(1) == null  // => False
Option.Some(1) == Option.None  // => False
Option.None == null  // => true

Access the option imperatively

Option<int> option = 1;
if (option.TryGetValue(out var value))
    return value.ToString();
else
    return "Empty";

Option<int> option = 1;
if (option.HasValue)
    return option.Value.ToString();
else
    return "Empty";

Option<int> option = 1;
var v = option.ValueOrDefault;
var v2 = option.ValueOr(0);
var v3 = option.ValueOr(() => 0); // Deferred factory method (if expensive)
}

Access and transform the option functionally

Pattern matching

Option<int> option = 1;
return option
    .Match(
        None: () => "Empty",
        Some: value => value.ToString()); // Also supports statements
}

Option<int> option = 1;
return option
    .Match()
    .None(() => "Empty")
    .Some(1, () => "One")
    .Some(value => value.ToString())
    .Result(); // Also supports statements

LINQ

Option<int> option = 1;
return option
    .Where(x => x == 1)
    .Select(x => x + 1)
    .SelectMany(x => x == 2 ? Option.Some(x) : Option.None)
    .DefaultIfEmpty(0)
    .Single();