StateObject.swift

// Version 1: Using initializer directly

struct ContentView: View {
    @State var count = 0
    let timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()

    var body: some View {
        VStack {
            Text("container: \(count)")
                .padding()
                .onReceive(timer) { _ in
                    self.count += 1
                }
            Subview(count)
        }
    }
}

struct Subview: View {
    @StateObject var foo: Foo

    init(_ count: Int) {
        _foo = StateObject(wrappedValue: Foo(count))
        print("init subview \(count)")
    }

    var body: some View {
        Text("subview: \(foo.count)")
    }
}

final class Foo: ObservableObject {
    let count: Int

    init(_ count: Int) {
        self.count = count
        print("init foo \(count)")
    }

    deinit {
        print("deinit foo \(count)")
    }
}

StateObject2.swift

// Version 2: Using generated initializer

struct ContentView: View {
    @State var count = 0
    let timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()

    var body: some View {
        VStack {
            Text("container: \(count)")
                .padding()
                .onReceive(timer) { _ in
                    self.count += 1
                }
            Subview(foo: Foo(count))
        }
    }
}

struct Subview: View {
    @StateObject var foo: Foo

    var body: some View {
        Text("subview: \(foo.count)")
    }
}

final class Foo: ObservableObject {
    let count: Int

    init(_ count: Int) {
        self.count = count
        print("init foo \(count)")
    }

    deinit {
        print("deinit foo \(count)")
    }
}

What get printed

init subview 0
init foo 0
init subview 1
init subview 2
init subview 3