Example

example.swift

import Foundation

struct ToDo : Identifiable, Equatable {
    let id: UUID
    var title: String
    var done: Bool
}

let id = UUID()
let todo = ToDo(id: id, title: "value1", done: false)

struct ToDoState : Equatable {
    var todos: [ToDo] = [
        todo,
        .init(id: .init(), title: "value2", done: false)
    ]
    var completedToDos: [ToDo]  {
        get {
            return todos.filter { $0.done }
        }
    }
    var unCompletedToDos: [ToDo]  {
        get {
            return todos.filter { !$0.done }
        }
    }
}

var state = ToDoState()
func run() {
    print("before: ", state) //
    if let index = state.todos.firstIndex(of: todo) {
        state.todos[index].done = !state.todos[index].done
    }
    print("after: ", state)
}

run()

// before:  ToDoState(todos: [__lldb_expr_11.ToDo(id: C46A21CF-32B2-496D-B151-48B3918BF885, title: "value1", done: false), __lldb_expr_11.ToDo(id: 78768BBC-F056-4862-817E-C7140FA4064A, title: "value2", done: false)])

// after:  ToDoState(todos: [__lldb_expr_11.ToDo(id: C46A21CF-32B2-496D-B151-48B3918BF885, title: "value1", done: true), __lldb_expr_11.ToDo(id: 78768BBC-F056-4862-817E-C7140FA4064A, title: "value2", done: false)])