Say hello to fennecs!

Let's start with a simple "Hello, World!" example to get you familiar with the basics of fennecs.

• defining Components
• spawning Entities
• compiling Queries (and using them!)

Defining Components

First, we define a simple Name component to store a string value. And let's sprinkle on a little 💫 raffinésse 💫 with a conversion operator... (it's a surprise tool that will help us later!)

internal readonly struct Name(string value)
{
    public static implicit operator Name(string value) => new(value);
    public override string ToString() => value;
}

Weird syntax?

The struct uses a Primary Constructor, but you can also write an old-style explicit one and an auto-property for value; or a public field.

Next, we declare two empty Tag components that will act as labels, Human and Fennec, to tag our Entities semantically:

internal readonly struct Human;
internal readonly struct Fennec;

Creating Entities

Next, we create a new World to hold our entities and components, and spawn a few Entities with a Name component, and with tags to denote their species:

var world = new World();

var fennec = world.Spawn()
      .Add<Fennec>()
      .Add<Name>("Erwin"); // Erwin is a Fennec!

var human1 = world.Spawn()
      .Add<Human>()
      .Add<Name>("Junno"); // Conversion operator makes these so readable!

var human2 = world.Spawn()
      .Add<Human>()
      .Add<Name>("Avinash"); // Feels good!

Querying Entities

Now, let's create two kinds of query to find all entities with a Name and run it to print a greeting for each entity. We also want to only match entities with a Fennec - in our case we can do it by inclusion or exclusion.

"Yo! This is fennecs, not human ecs!"

var noHumans = world.Query<Name>()
    .Not<Human>()
    .Stream();

noHumans.For(static (ref Name name) =>
{
    Console.WriteLine($"Hello, {name}!");
});

"Hmm, human ecs?! ... I like it."

var onlyFennecs = world.Query<Name>()
    .Has<Fennec>()
    .Stream();

onlyFennecs.For(static (ref Name name) =>
{
    Console.WriteLine($"Hello, {name}!");
});

Expected Output

When you run this code, you should see the following output:

Hello, Erwin!
Hello, Erwin!

---

"OnlyFennecs... ... !"