Why does Get() always return pointer type?

[setanarut]

Why does Get() always return pointer type? (*float64) Even though I created float64 type component.

package main

import (
	"fmt"

	"github.com/yohamta/donburi"
)

func main() {
	w := donburi.NewWorld()
	health := donburi.NewComponentType[float64]()
	e := w.Entry(w.Create(health))
	health.SetValue(e, 5.0)
	fmt.Printf("%T\n", health.Get(e))
	// *float64
}

[yohamta]

Hello, it's because donburi stores component data as pointer. I think we can add GetValue() method to get value instead of pointer. What do you think?

[setanarut]

I've read that using pointer type is slower for primitive types. (in terms of memory access speed). Also there is no donbori guide for singleton components. I don't know what's going on behind the scenes.

[yohamta]

I see your point. Currently, donburi stores component data as unsafe.pointer here:

donburi/internal/storage/storage.go

Lines 9 to 16 in ba79e83

	// Storage is a structure that stores the pointer to data of each component.
	// It stores the pointers in the two dimensional slice.
	// First dimension is the archetype index.
	// Second dimension is the component index.
	// The component index is used to access the component data in the archetype.
	type Storage struct {
	storages [][]unsafe.Pointer
	}

I am a bit unsure about the impact of memory access speed, but perhaps we can experiment to see if it's significant enough to make changes. Regarding singleton components, Donburi does not have a dedicated API. Do you have any thoughts or ideas on that?

[setanarut]

I see your point. Currently, donburi stores component data as unsafe.pointer here:

donburi/internal/storage/storage.go

Lines 9 to 16 in ba79e83

	// Storage is a structure that stores the pointer to data of each component.
	// It stores the pointers in the two dimensional slice.
	// First dimension is the archetype index.
	// Second dimension is the component index.
	// The component index is used to access the component data in the archetype.
	type Storage struct {
	storages [][]unsafe.Pointer
	}

I am a bit unsure about the impact of memory access speed, but perhaps we can experiment to see if it's significant enough to make changes. Regarding singleton components, Donburi does not have a dedicated API. Do you have any thoughts or ideas on that?

I changed my mind. I don't think it will affect speed for a few thousand Entities. In terms of syntax, it would be nice to have GetValue().

---

Donburi does not have a dedicated API. Do you have any thoughts or ideas on that?

A helper function can be added for the singleton component. For example, when e1 is changed, all entities with the same component will also change. I think there is currently no way to do this without using a variable and Set() and SetValue() .

package main

import (
	"fmt"

	"github.com/yohamta/donburi"
)

func main() {
	a := "A"
	w := donburi.NewWorld()
	Str := donburi.NewComponentType[string]()

	e1 := w.Entry(w.Create(Str))
	e2 := w.Entry(w.Create(Str))
	Str.Set(e1, &a)
	Str.Set(e2, &a)

	Str.SetValue(e1, "B")

	fmt.Println(*Str.Get(e1))
	fmt.Println(*Str.Get(e2))
	// B
	// B
}

Pseudo code in my mind

	Str := donburi.NewSingletonComponentType[string]("A")

	e1 := world.Entry(world.Create(Str))
	e2 := world.Entry(world.Create(Str))

	Str.SetValue(e1, "B")

	fmt.Println(*Str.Get(e1))
	fmt.Println(*Str.Get(e2))
	// B
	// B

[yohamta]

Thanks for the example. The idea of a singleton component feature is indeed interesting. I believe it may be feasible to develop a features/singleton package which would enable arbitrary component to be treated as a singleton (transparently). What do you think?

[setanarut]

Thanks for the example. The idea of a singleton component feature is indeed interesting. I believe it may be feasible to develop a features/singleton package which would enable arbitrary component to be treated as a singleton (transparently). What do you think?

I don't think this is a very important feature, but it is useful for legible code. Also, forcing to use global variables is against ECS design.

[yohamta]

By the way, bevy, an game engine for Rust that uses ECS architecture, has a concept called Resource. This concept allows for handling data without an entity, and the data is automatically passed to systems.