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Fluentify

Fluentify is a .NET Roslyn Source Generator designed to automate the creation of Fluent APIs. This tool enables engineers to rapidly develop rich, expressive, and maintainable APIs with ease. Utilizing Fluentify allows for cleaner code, easier maintenance, and more expressive interactions within your C# .NET applications.

If you are unfamiliar with Fluent Builder pattern, please review Building Complex Objects in a Simple Way with C# by Gui Ferreira. Using its example, with Fluentify, we can transform how we configure movies from this:

var movie = new Movie
{
    Genre = Genre.SciFi,
    Title = "Star Trek: First Contact",
    ReleasedOn = new DateOnly(1996, 12, 13),
    Actors =
    [
        new Actor
        {
            Birthday = 1940,
            FirstName = "Patrick",
            Surname = "Stewart",
        },
    ],
};

to this:

var movie = new Movie()
   .OfGenre(Genre.SciFi)
   .WithTitle("Star Trek: First Contact")
   .ReleasedOn(new DateOnly(1996, 12, 13))
   .WithActors(actor => actor
       .WithFirstName("Patrick")
       .WithSurname("Stewart")
       .BornIn(1940));

This document will use the Movie example to describe how the features of Fluentify can be used to make the illustrated use of the Fluent Builder pattern possible.

Installation

To install Fluentify, use the following command in your package manager console:

install-package Fluentify

Usage

Fluentify automatically creates extension methods for each property on types that have the Fluentify attribute, supporting both class and record types.

Record Type Usage

[Fluentify]
public record Actor(int Birthday, string FirstName, string Surname);

[Fluentify]
public record Movie(Actor[] Actors, Genre Genre, DateOnly ReleasedOn, string Title);

Marking the record type as partial will generate a default constructor, allowing for the record to be instantiated without first initializing the properties.

[Fluentify]
public partial record Actor(int Birthday, string FirstName, string Surname);

// Allows for instantiation without property initialization
var actor = new Actor();
...

Class Type Usage

[Fluentify]
public class Actor
{
    public int Birthday { get; init; }
    public string FirstName { get; init; }
    public string Surname { get; init; }
}

[Fluentify]
public class Movie
{
    public Actor[] Actors { get; init; }
    public Genre Genre { get; init; }
    public DateOnly ReleasedOn { get; init; }
    public string Title { get; init; }
}

A class type is supported as long as the type has an accessible default constructor (implicit or explicit).

Immutability

The generated extension methods preserve immutability, providing a new instance with the specified value applied to the associated property.

var original = new Actor { Birthday = 1942 };
var @new = original.WithBirthday(1975);

Console.WriteLine(original.Birthday); // Displays 1942
Console.WriteLine(@new.Birthday);     // Displays 1975

Auto Instantiation

The value associated with a given property can be automatically instantiated, as long as that type associated with the property adheres to the new() constraint. A second extension method is generated for the property, accepting a Func<T, T> delegate as its parameter, which allows for the newly instantiated value to be configured before being applied.

_ = movie.WithActors(actor => actor
    .WithBirthday(1940)
    .WithFirstName("Patrick")
    .WithSurname("Stewart"));

Collection Parameterization

Values can be appended to a list as long as the property type is T[], IEnumerable<T>, IReadOnlyCollection<T>, IReadOnlyList<T>. Property types that derive from ICollection<T> and adhere to the new() constraint are also supported. Unlike with scalar properties, the generated extension method accepts a params T[], allowing for one or more values to be specified in a single invocation.

var original = new Movie { Actors = [picard] };
var @new = original.WithActors(worf);

Console.WriteLine(original.Actors.Length); // Displays 1
Console.WriteLine(@new.Actors.Length);     // Displays 2

Custom Descriptors

By default, Fluentify will generate an extension method for each property using the With{Property Name} pattern for all types, with the exception of bool, which defaults to the declared name of the property.

The name used can be customized via the Descriptor attribute. When a descriptor is provided that is deemed acceptable as a method name to the compiler, it is applied to the extension method. When no descriptor is provided, the declared name of the property used.

Record Type Usage

[Fluentify]
public partial record Actor(
    [Descriptor("BornIn")] int Birthday,
    string FirstName,
    string Surname);

[Fluentify]
public partial record Movie(
    Actor[] Actors,
    [Descriptor("OfGenre")] Genre Genre,
    [Descriptor] DateOnly ReleasedOn,
    string Title);

Class Type Usage

[Fluentify]
public class Actor
{
    [Descriptor("BornIn")]
    public int Birthday { get; init; }
    
    public string FirstName { get; init; }

    public string Surname { get; init; }
}

[Fluentify]
public class Movie
{
    public Actor[] Actors { get; init; }
    
    [Descriptor("OfGenre")] 
    public Genre Genre { get; init; }
    
    [Descriptor]
    public DateOnly ReleasedOn { get; init; }
    
    public string Title { get; init; }
}

This allows for greater alignment with domain semantics:

var movie = new Movie()
   .OfGenre(Genre.SciFi)
   .WithTitle("Star Trek: First Contact")
   .ReleasedOn(new DateOnly(1996, 12, 13))
   .WithActors(actor => actor
       .WithFirstName("Patrick")
       .WithSurname("Stewart")
       .BornIn(1940));

Property Exclusion

Specific properties can be excluded from generating Fluentify extension method(s) using the Ignore attribute:

Record Type Usage

[Fluentify]
public record Actor([Ignore] int Birthday, string FirstName, string Surname);

Class Type Usage

[Fluentify]
public class Actor
{
    [Ignore]
    public int Birthday { get; init; }
    public string FirstName { get; init; }
    public string Surname { get; init; }
}

This will result in an error if you try to use the ignored property in the chain:

_ = actor
    .WithBirthday(1975) // IntelliSense Error: 'Actor' does not contain a definition for 'WithBirthday'
    .WithFirstName("Avery")
    .WithSurname("Brooks");

Analyzers

Fluentify includes several analyzers to assist engineers with its usage. These are:

Building a Service

Combining Fluentify with additional, custom methods, can assist with the construction of complex types. For example:

public class MyService
{
    public MyService(string connectionString, TimeSpan timeout)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(connectionString);
        ArgumentOutOfRangeException.ThrowIfLessThan(timeout.TotalSeconds, 1);

        ConnectionString = connectionString;
        Timeout = timeout;
    }

    public string ConnectionString { get; }

    public TimeSpan Timeout { get; }
}

[Fluentify]
public partial record MyServiceBuilder(
    [Descriptor("ConnectsTo")] string ConnectionString,
    [Descriptor("Waits")] int Timeout)
{
    public static MyServiceBuilder Default => new();
    
    public MyService Build()
    {
        return new MyService(ConnectionString, TimeSpan.FromSeconds(Timeout));
    }
}

In this example, a new instance of MyService can be created as follows:

MyService service = MyServiceBuilder
    .Default
    .ConnectsTo("Some Connection String")
    .Waits(30)
    .Build();

Contributing

Contributions are welcome - see the CONTRIBUTING.md file for details.

License

This project is licensed under the MIT License - see the LICENSE.md file for details.