Allow using composites as function parameters in structures

Question content

Let's say I'm making something like a game engine.

I need a GameObject structure to define some event handlers:

type GameObject struct {
    transform        Transform
    animatedMesh     AnimatedMesh
    updateHandler    func(self GameObjectGetter)
    onCreateHandler  func(self GameObjectGetter)
    onDestroyHandler func(self GameObjectGetter)
}


func (g GameObject)getGameObject() GameObject {
    return g
 }

 type GameObjectGetter interface {
    getGameObject() GameObject
 }

Then when I initialize some specific game objects, I want to define the handler as a custom function:

g.updateHandler = func(self FishGameObject) {  // Error here
    self.tailMotionSpeed = self.boid.acceleration.Normalize().Len()
}

Please note that tailMotionSpeed and boid are not members of GameObject. They are members of struct FishGameObject, which has some custom properties and an anonymous GameObject:

type FishGameObject struct {
    leftFinPosition  float32
    rightFinPosition float32
    tailMotionSpeed  float32
    boid             Boid
    GameObject
}

If I specify the parameter as GameObjectGetter, I get the error self.tailMotionSpeed ​​undefined (type GameObjectGetter has no field or method tailMotionSpeed) , and I get the error cannot use handler (type func (variable of self FishGameObject) )) as the value of func(self GameObjectGetter) in the struct literal (if I specify the parameter as FishGameObject). what do I do?

Correct answer

What you want to do is not possible in Go the way you want to do it. However, you can do this:

Define GameObject as interface:

type GameObject interface {
   GetTransform() *Transform
   GetAnimatedMesh() *AnimatedMesh
   SetUpdateHandler(func(GameObject))
   UpdateHandler() func(GameObject)
   ...
}

You can define a BaseGameObject:

type BaseGameObject struct {
    transform        Transform
    animatedMesh     AnimatedMesh
    updateHandler    func(GameObject)
    onCreateHandler  func(GameObject)
    onDestroyHandler func(GameObject) 
}

Define all methods so that BaseGameObject becomes GameObject.

Then, define FishGameObject like you did, but

fish.SetUpdateHandler(func(self GameObject) {  
    fish:=self.(*FishGameObject)
     ...
   })

You should also use pointer receivers for all methods.

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