Intersection types for C#!

Installation

Install IotaLambda.Intersection to each project containing IntersectionTypes. This will make a source generator to be executed for those types.

Install-Package IotaLambda.Intersection

In a nutshell

Consider the following model:

interface IPokemon { string GetNickName(); void GetHp(); void TakeDamage(int damage); } interface IFireType { void AttackWithFlamethrower(IPokemon enemy); } interface IFlyingType { void FlyTo(string city); } class Charizard : IPokemon, IFireType, IFlyingType { int hp = 120; string location = "Cerulean City"; public string GetNickName() => "Lizardon"; public void GetHp() => hp; public void TakeDamage(int damage) => hp -= damage; public void AttackWithFlamethrower(IPokemon enemy) => enemy.TakeDamage(50); public void FlyTo(string city) => location = city; }

You can create intersection types such as:

[IntersectionType] readonly struct SFirePokemon : IPokemon, IFireType; // S as in Shape [IntersectionType] readonly struct SFlyingPokemon : IPokemon, IFlyingType;

and use them as types as usual without having to colour your codebase with generic constraints like where TPokemon : IPokemon, IFlyingType:

var ash = new Ash(); var charizard = new Charizard(); ash.Fly_Better(SFlyingPokemon.From(charizard), "Lavender Town"); public class Ash { public bool Fly_Better(SFlyingPokemon pokemon, string city) // No need to define generic constraints, as the intersection type already covers that! { if (pokemon.GetHp() <= 0) return false; pokemon.FlyTo(city); DescribeTravel("flew", pokemon.AsComponent<IPokemon>(), city); // Use `AsComponent<>` to get one of the components without boxing. `AsComponent<>`s are statically typed overloads for each component! return true; } public bool Fly_Normal<TPokemon>(TPokemon pokemon, string city) where TPokemon : IPokemon, IFlyingPokemon { if (pokemon.GetHp() <= 0) return false; pokemon.FlyTo(city); DescribeTravel("flew", pokemon, city); return true; } void DescribeTravel(string verb, IPokemon pokemon, string city) { System.Console.WriteLine($"Ash {verb} to {city} with {pokemon.GetNickName()}.") } }