OptRes 6.1.2

dotnet add package OptRes --version 6.1.2
NuGet\Install-Package OptRes -Version 6.1.2
This command is intended to be used within the Package Manager Console in Visual Studio, as it uses the NuGet module's version of Install-Package.
<PackageReference Include="OptRes" Version="6.1.2" />
For projects that support PackageReference, copy this XML node into the project file to reference the package.
paket add OptRes --version 6.1.2
#r "nuget: OptRes, 6.1.2"
#r directive can be used in F# Interactive and Polyglot Notebooks. Copy this into the interactive tool or source code of the script to reference the package.
// Install OptRes as a Cake Addin
#addin nuget:?package=OptRes&version=6.1.2

// Install OptRes as a Cake Tool
#tool nuget:?package=OptRes&version=6.1.2


C# library for option and lightweight-result types:

  • Opt<T>: Some(T) or None;
  • Res: Ok or Err(message);
  • Res<T>: Ok(T) or Err(message).

In order to enable the types glboally, add the following in project's global usings file:

global using OptRes;
global using static OptRes.Extensions;

Alternatively, the scope can be limited to a file by adding the following in the particular file:

using OptRes;
using static OptRes.Extensions;

Complete auto-generated documentation can be found here: sandcastle-documentation.


Opt<T> is a readonly struct that can be either of the two variants:

  • Some(T): holding a nonnull (!) value of T, or
  • None: nothing, absense of data.

Despite of the improvements in the language with nullable, the checks are still in warning level.

The type Opt<T> aims to:

  • make absense of data and optionality of a method argument explicit; and,
  • getting closer to fluent, railway oriented programming in C# (see Scott Wlaschin's talk).

Some of the features are illustrated in the Player record below; the code can be found in Examples/Player.cs.

record Player(
    string Name,
    int Wins,
    Opt<string> Nickname = default,     // stating explicitly that not all players have a nickname
    Opt<string> EmailAddress = default  // default of Opt<T> is None<T>()
    public void Greet()
        // UnwrapOr returns the underlying value if IsSome; the fallback value otherwise.
        // When the fallback value is expensive (requires a database query, for instance), lazy version can be used:
        // Nickname.UnwrapOr(() => Name)
        string greeting = string.Format("Hey {0}", Nickname.UnwrapOr(Name));

        // alternative uses of UnwrapOr, Match, IsSome & Unwrap
        Assert(Nickname.UnwrapOr(Name) == Nickname.Match(whenSome: nick => nick, whenNone: Name));
        Assert(Nickname.UnwrapOr(Name) == (Nickname.IsSome ? Nickname.Unwrap() : Name));
    public bool HasNickname()
        => Nickname.IsSome; // = !IsNone

    public Opt<int> NicknameLength()
        // Map into other types by chaining results, while the IsNone checks are internally handled:
        // * if Nickname.IsSome, the result will be the Some(Nickname.Unwrap().Length);
        // * None<int>() otherwise.
        return Nickname.Map(nick => nick.Length);

    public void SendEmail(string message)
        // send only if the player has an email address
        EmailAddress.Do(emailAddr => Console.WriteLine($"fake-sending {message} to {emailAddr}"));

    public int Score()
        // assume having a nickname provides +5 wins.
        return Wins + Nickname.Match(whenSome: _ => 5, whenNone: 0);

    public void RemindToAddEmail()
        // do only if IsNone
        EmailAddress.DoIfNone(() => Console.WriteLine("you may add your email address for ..."));

    public Opt<Player> FindMatch(IEnumerable<Player> others)
        // linq alternative to FirstOrDefault that would return null in absent case.

        // there also exist the following extension variants on IEnumerable<Opt<T>>:
        // * Do & DoIfNone
        // * Map & FlatMap
        // * Try & TryMap
        // * Match & MatchDo

        return others.FirstOrNone(x => x.Score() == Score());
    public Opt<string> FindNicknameOfMatch(IEnumerable<Player> others)
        // FindMatch(others).Map(x => x.Nickname) => would have returned Opt<Opt<string>>.
        // FlatMap allows to escape the nesting

        // Alternatively, one can use the Flatten method:
        // FindMatch(others).Map(x => x.Nickname).Flatten();
        return FindMatch(others).FlatMap(x => x.Nickname);
    public Opt<char> FindInitialOfNicknameOfMatch(IEnumerable<Player> others)
        // you may keep chaining:
        // * if any step returns Non, it will be carried on to the end bypassing succeeding methods
        // * the output will be IsSome only if all steps return Some.
        return FindMatch(others)
            .FlatMap(x => x.Nickname)
            .Map(nick => nick[0]);

    // static methods
    public static Opt<string> ValidateEmail(string inputEmailAddress)
        // the value will be Some only if the validation condition is true.
        return SomeIf(inputEmailAddress.Contains('@'), inputEmailAddress);
    public static void Parsers()
        // string & ReadOnlySpan<char> has ParseOrNone extensions for primitives
        Opt<int> nbGames = "12".ParseIntOrNone();
        Opt<bool> isWin = "false".ParseBoolOrNone();
        Opt<double> elapsedSeconds = "42.42".ParseDoubleOrNone();

        // and general parser for any T with lambda parser
        Opt<bool> isWinLambda = "Yes".TryParseOrNone(str => StringComparer.OrdinalIgnoreCase.Equals(str, "yes"));
    public static List<string> Nicknames(IEnumerable<Player> players)
        // will create a list of all nicknames, skipping None's.
        return players.Select(x => x.Nickname).UnwrapSomes().ToList();
    public static Opt<Player> GetPlayerByNickname(Dictionary<string, Player> dictNickPlayer, string nickname)
        // (similar to FirstOrNone or LastOrNone)
        // alternative to GetValueOrDefault method which would have returned null in absent case.

        return dictNickPlayer.GetOpt(nickname);

    // static methods - constructors
    public static Player Dendi()
        return new Player(
            Name: "Dendi",
            Wins: 0,
            Nickname: Some("NaVi"),         // static constructor for Some variant.
            EmailAddress: None<string>()    // static constructor for None variant; can also use default

Res and Res<T>

Res and Res<T> are simplified result types, where the error variant holds only the error message.

Res has the following two variants:

  • Ok: just a flag stating that the state is okay,
  • Err(message): an error state with the corresponding error message.

Res<T>, on the other hand, can hold data and has the following variants:

  • Ok(T): okay state holding a non-null (!) value of T,
  • Err(message): an error state with the corresponding error message.

These result types aim to:

  • make possibility of failures explicit;
  • avoiding (hiding) the verbose try-catch blocks, as well as, throwing exceptions,
  • getting closer to fluent, railway oriented programming in C#.

Some of the features are illustrated in the example files Examples/ExampleRes.cs and Examples/ExampleResT.cs.

Product Compatible and additional computed target framework versions.
.NET net6.0 is compatible.  net6.0-android was computed.  net6.0-ios was computed.  net6.0-maccatalyst was computed.  net6.0-macos was computed.  net6.0-tvos was computed.  net6.0-windows was computed.  net7.0 was computed.  net7.0-android was computed.  net7.0-ios was computed.  net7.0-maccatalyst was computed.  net7.0-macos was computed.  net7.0-tvos was computed.  net7.0-windows was computed.  net8.0 was computed.  net8.0-android was computed.  net8.0-browser was computed.  net8.0-ios was computed.  net8.0-maccatalyst was computed.  net8.0-macos was computed.  net8.0-tvos was computed.  net8.0-windows was computed. 
Compatible target framework(s)
Included target framework(s) (in package)
Learn more about Target Frameworks and .NET Standard.
  • net6.0

    • No dependencies.

NuGet packages (6)

Showing the top 5 NuGet packages that depend on OptRes:

Package Downloads

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Simple excel table to csv converter.


Jagged array representations, wrapping different underlying data types by a functional approach in order to achieve a unified collection type.


Concise mathematical modeling library in C#, allowing to code models that are not different nor longer than those on the paper.


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GitHub repositories

This package is not used by any popular GitHub repositories.

Version Downloads Last updated
6.1.2 480 1/21/2023
6.1.1 539 1/3/2023
6.1.0 262 1/3/2023
6.0.0 428 12/28/2022