C# 泛型約束實戰（二）：IComparable 約束驅動的可排序鏈表完整實作

編輯：關於C語言

執行結果展示


Adding: 2 1 2 6 1 5 9 0 5
Retrieving collections…
Integers: 0,1,1,1,2,2,5,5,6,9
Employees: George, John, Paul, Ringo

約束設計核心

Employee 實作 IComparable<Employee>


public class Employee : IComparable
{
    private string _name;
    public Employee(string name) => _name = name;

    public int CompareTo(Employee other) => _name.CompareTo(other._name);
    public bool Equals(Employee other) => _name == other._name;
    public override string ToString() => _name;
}

Node 約束鏈：節點與資料雙重約束


// 節點本身可比較，且要求資料型別 T 也可比較
public class Node : IComparable> where T : IComparable
{
    public T Data { get; }
    public Node Next { get; private set; }
    public Node Prev { get; private set; }

    public int CompareTo(Node other) => Data.CompareTo(other.Data); // 安全：編譯期保證 T 實作 IComparable
}

LinkedList 繼承約束


public class LinkedList where T : IComparable
{
    private Node _head;

    public void Add(T data)
    {
        var newNode = new Node(data);
        _head = _head == null ? newNode : _head.Add(newNode);
    }
}

遞迴插入邏輯


public Node Add(Node newNode)
{
    if (this.CompareTo(newNode) > 0) // 新節點較小，插入前方
    {
        newNode.Next = this;
        if (this.Prev != null)
        {
            this.Prev.Next = newNode;
            newNode.Prev = this.Prev;
        }
        this.Prev = newNode;
        return newNode; // 新頭節點
    }
    else // 插入後方
    {
        if (this.Next != null)
            this.Next.Add(newNode); // 遞迴
        else
        {
            this.Next = newNode;
            newNode.Prev = this;
        }
        return this; // 維持原頭節點
    }
}

約束帶來的安全性保證

無約束風險	有約束保證
執行時才發現型別不支援比較	編譯期直接報錯
需防禦性檢查 `is IComparable`	直接呼叫 `CompareTo` 無需判斷
文件說明易過時	型別系統強制執行契約

進階約束模式


// 多重約束
public class Repository where T : class, IEntity, new()

// 建構式約束
public class Factory where T : new()

// 實值/參考型別約束
public class StructProcessor where T : struct
public class ClassProcessor where T : class

// 不受約束型別參數
public class Unconstrained { }