c# - 作为装饰器的集合 : pseudo-code implementation proposal

Question

同时等待 question 的答复我想讨论可能的实现计划/细节，或者总体上回答实现以下内容有多困难以及需要哪些工具/技术:

(摘自所提到的问题):

Suppose you need to implement many (sub)types of collections. One of the aspects is storage-related: list, array etc, while the other is behavior-related: ordered, remove only, observable (the one that fires an event upon every change) etc.

Obviously (again), the requirement maps directly to the well-known Decorator design pattern, where the storage-related aspect (list, array) will be decorated by multiple behavioral (ordered, observable etc).

到目前为止，我想用(类似 Java 的)伪代码提出一些相当短的实现，同时询问是否可以用 Java 或 C# 实现以下内容，如果不能，则可以用任何其他现代编程语言实现:

每个集合必须支持的基本接口(interface):

interface Collection {
    [mutator]
    public void add(object o);

    [mutator]
    public void remove(object o);

    [accessor]
    public object get(int i);
}

存储方面:

列表实现:

class List : Collection {
    [mutator]
    public void add(object o) { ... }

    [mutator]
    public void remove(object o) { ... }

    [accessor]
    public object get(int i) { ... }
}

数组实现:

class Array : Collection {
    [mutator]
    public void add(object o) { ... }

    [mutator]
    public void remove(object o) { ... }

    [accessor]
    public object get(int i) { ... }
}

行为方面:

线程安全装饰器:

typename<T> : where T is Collection
class ThreadSafe : Collection {
    private T m_source;
    private object m_lock = new object();

    [mutator]
    public void add(object o) { 
        using (m_lock) {
            m_source.add();
        }
    }

    [mutator]
    public void remove(object o) { ... }

    [accessor]
    public object get(int i) { ... }
}

可观察装饰器:

class ChangeEvent {
    public Collection Source { get; private set; }
    public Method UpdateType { get; private set; }
}

interface Observer {
    public notifyChange(ChangeEvent e);
}

typename<T> : where T is Collection
class Observable : Collection {
    public Observer Observer { get; set; } // additional property
    private T m_source;

    [mutator]
    public void add(object o) {
        if (Observer != null) {
            var event = new ChangeEvent() { Source = this, UpdateType = GetCurrentMethod() };
            Observer.notifyChange(event);
        }
        m_source.add(o);
    }

    [mutator]
    public void remove(object o) { ... }

    [accessor]
    public object get(int i) { ... }
}

有序装饰器:

typename<T> : where T is Collection
class Ordered : Collection {
    private T m_source;

    [mutator]
    public void add(object o) {
        int idx = findProperPosition(); // assumed possible using the base Collection interface
        ...
        m_source.add(o);
    }

    [mutator]
    public void remove(object o) { ... }

    [accessor]
    public object get(int i) { ... }
}

只读装饰器:

typename<T> : where T is Collection
class ReadOnly : Collection {
    private T m_source;

    [mutator]       
    public void add(object o) { throw IllegalOperationException(...); }

    [mutator]
    public void remove(object o) { throw IllegalOperationException(...); }

    [accessor]
    public object get(int i) { return m_source.get(i); }
}

到目前为止，上面只是伪代码，但目标是使客户端代码能够构造多种集合，以便每种集合可以精确地组合任意数量的存储方面>行为相关方面。如果能够在编译时构造这些复合类型，并且即使在运行时也能非常方便地生成这些复合类型，那就太好了。

问题是(任何现代编程语言都重要)如何？

Answer 1

我不明白你不明白的是哪一方面。 Java 集合已经有这个并且源是公开的。它们具有线程安全且不可修改的装饰器。此外，许多类型都有外观方法，例如“asList()”。

鉴于此，您的问题还剩下什么？

如何将未订购的东西制作成订购的？比如，如何创建一个将 HashMap 转换为 LinkedHaskMap 的装饰器？这样的装饰器可以使用内部数据结构来构建以维持顺序。