迭代器与组合模式

迭代器模式

Definition: 提供一个接口顺序访问一个聚合对象的元素，而不暴露其内部实现细节

在C#中体现为IEnumerator接口的Current, MoveNext(), Reset()

迭代集合时，将不同的集合类封装起来，只对外暴露一个迭代器

组合模式

Definition: 允许将对象组合成树型结构来表现「整体 / 部分」层次结构

也就是说，一个聚合对象的元素可以是元素（leaf）或者子聚合对象


    public abstract class MenuComponent {
        // Operations
        public virtual void Operation() {
            throw new NotSupportedException();
        }
		
        // Components related
        public virtual void Add(MenuComponent menuComponent) {
            throw new NotSupportedException();
        }
		
        public virtual void Remove(MenuComponent menuComponent) {
            throw new NotSupportedException();
        }
		
        public virtual MenuComponent GetChild(int index) {
            throw new NotSupportedException();
        }
    }

    public class Menu : MenuComponent {
        public List<MenuComponent> MenuComponents;

        public override void Operation() {
            foreach (var com in MenuComponents) {
                com.Operation();
            }
        }

        public override void Add(MenuComponent menuComponent) {
            MenuComponents.Add(menuComponent);
        }
        
        public override void Remove(MenuComponent menuComponent) {
            MenuComponents.Remove(menuComponent);
        }

        public override MenuComponent GetChild(int index) {
            return MenuComponents[index];
        }
    }

    public class MenuItem : MenuComponent {
        private string name;
        private string description;

        public MenuItem(string name, string description) {
            this.name = name;
            this.description = description;
        }
        public override void Operation() {
            Console.WriteLine($"{name}: {description}")
        }
    }