Need design ideas for resultbuilder and chained method attributes; making a builder for RealityKit entities/scenes

I'm playing with resultbuilders and methods chaining to create declarative spatial scenes within a RealityKit RealityView.

In one case I'm struggling with getting to a cleanest declaration of a mesh entity (basic geormetry shape, color, metalic, etc). I tried a version that took in a SimpleMaterial, modified it and output a new simple material is the adjustment of the chained modified. I had issues with the getters and inits if simple material not having compatible types.

I'm looking at another appoach of having a builder syntax, but it its not as clean and error prone to use.

I'm open to all suggestions and feedback.

I will push this to public git when done-ish.

extension ModelComponent {
    struct Builder {
        var mesh: MeshResource?
        var color: UIColor?
        var isMetallic: Bool = false
        func build() -> ModelComponent {
            let materialColor = color ?? .white // Default color
            let material = SimpleMaterial(color: materialColor, isMetallic: isMetallic)
            let meshResource = mesh ?? MeshResource.generateBox(size: 0.1) // Default mesh
            return ModelComponent(mesh: meshResource, materials: [material])
    var builder: Builder {
        return Builder()

extension ModelComponent.Builder {
    mutating func box(_ size: Float) -> ModelComponent.Builder {
        self.mesh = MeshResource.generateBox(size: size)
        return self
    mutating func color(_ color: UIColor) -> ModelComponent.Builder {
        self.color = color
        return self
    mutating func metallic(_ isMetallic: Bool = true) -> ModelComponent.Builder {
        self.isMetallic = isMetallic
        return self

// Usage
let modelComponent = ModelComponent().builder