Split GetRef into multiple methods

src/gaemstone/ECS/EntityBase.cs

@@ -13,7 +13,9 @@ public abstract class EntityBase<TReturn>
 	public abstract T Get<T>();
 	public abstract T? MaybeGet<T>() where T : unmanaged;
 	public abstract T? MaybeGet<T>(T _ = null!) where T : class;
-	public abstract ref T GetRef<T>() where T : unmanaged;
+	public abstract ref T GetMut<T>() where T : unmanaged;
+	public abstract ref T GetRefOrNull<T>() where T : unmanaged;
+	public abstract ref T GetRefOrThrow<T>() where T : unmanaged;
 	public abstract void Modified<T>();
 
 	public abstract TReturn Set<T>(in T value) where T : unmanaged;

src/gaemstone/ECS/EntityBuilder.cs

@@ -70,7 +70,9 @@ public class EntityBuilder
 	public override T Get<T>() => throw new NotSupportedException();
 	public override T? MaybeGet<T>() => throw new NotSupportedException();
 	public override T? MaybeGet<T>(T _ = null!) where T : class => throw new NotSupportedException();
-	public override ref T GetRef<T>() => throw new NotSupportedException();
+	public override ref T GetMut<T>() => throw new NotSupportedException();
+	public override ref T GetRefOrNull<T>() => throw new NotSupportedException();
+	public override ref T GetRefOrThrow<T>() => throw new NotSupportedException();
 	public override void Modified<T>() => throw new NotImplementedException();
 
 	public override EntityBuilder Set<T>(in T value)

src/gaemstone/ECS/EntityRef.cs

@@ -81,11 +81,27 @@ public unsafe sealed class EntityRef
 		return (ptr != null) ? (T)((GCHandle)Unsafe.Read<nint>(ptr)).Target! : null;
 	}
 
-	public override ref T GetRef<T>()
+	public override ref T GetRefOrNull<T>()
+	{
+		var comp = Universe.LookupOrThrow<T>();
+		var @ref = ecs_ref_init_id(Universe, this, comp);
+		var ptr  = ecs_ref_get_id(Universe, &@ref, comp);
+		return ref (ptr != null) ? ref Unsafe.AsRef<T>(ptr) : ref Unsafe.NullRef<T>();
+	}
+
+	public override ref T GetRefOrThrow<T>()
+	{
+		ref var ptr = ref GetRefOrNull<T>();
+		if (Unsafe.IsNullRef(ref ptr)) throw new Exception(
+			$"Component {typeof(T)} not found on {this}");
+		return ref ptr;
+	}
+
+	public override ref T GetMut<T>()
 	{
 		var comp = Universe.LookupOrThrow<T>();
 		var ptr  = ecs_get_mut_id(Universe, this, comp);
-		if (ptr == null) throw new Exception($"Component {typeof(T)} not found on {this}");
+		// NOTE: Value is added if it doesn't exist on the entity.
 		return ref Unsafe.AsRef<T>(ptr);
 	}