World Entity Access

So far, we only used ecs.Query to access components. Component access in queries is highly efficient, but it does not provide access to the components of a specific entity. This is possible through ecs.World methods, or using a generic MapX (like generic.Map2 ) or generic.Map .

Getting components

For a given entity, components can be accessed using ecs.World.Get or generic.Map2.Get , respectively:

1world := ecs.NewWorld()
2
3builder := generic.NewMap2[Position, Heading](&world)
4entity := builder.New()
5
6pos, head := builder.Get(entity)
7
8_, _ = pos, head

 1world := ecs.NewWorld()
 2
 3posID := ecs.ComponentID[Position](&world)
 4headID := ecs.ComponentID[Heading](&world)
 5
 6entity := world.NewEntity(posID, headID)
 7
 8pos := (*Position)(world.Get(entity, posID))
 9head := (*Heading)(world.Get(entity, headID))
10
11_, _ = pos, head

Similarly, it is also possible to check if an entity has a given component with ecs.World.Has or generic.Map.Has , respectively:

1world := ecs.NewWorld()
2
3builder := generic.NewMap2[Position, Heading](&world)
4entity := builder.New()
5
6mapper := generic.NewMap[Position](&world)
7
8hasPos := mapper.Has(entity)
9_ = hasPos

1world := ecs.NewWorld()
2
3posID := ecs.ComponentID[Position](&world)
4headID := ecs.ComponentID[Heading](&world)
5
6entity := world.NewEntity(posID, headID)
7
8hasPos := world.Has(entity, posID)
9_ = hasPos

Note that we have to use generic.Map here, which is similar to generic.Map1 for a single component, but offers more functionality.

Unchecked access

The Get and Has methods shown above all have a companion GetUnchecked and HasUnchecked, which is faster, but should be used with care. Particularly, they do not check whether the entity is still alive. Like Get, they panic when called on a removed entity. However, for a removed and subsequently recycled entity, they lead to undefined behavior.

It is safe to use methods like ecs.World.GetUnchecked after a usual Get was used on the same entity:

 1world := ecs.NewWorld()
 2
 3posID := ecs.ComponentID[Position](&world)
 4headID := ecs.ComponentID[Heading](&world)
 5
 6entity := world.NewEntity(posID, headID)
 7
 8pos := (*Position)(world.Get(entity, posID))
 9head := (*Heading)(world.GetUnchecked(entity, headID))
10
11_, _ = pos, head

Note that, following this use case, generic MapX internally use ecs.World.GetUnchecked for all but the first component.