1. IEnumerable,IEnumerator

public class MyIEnumerableClass<T> : IEnumerable<T>,IEnumerator<T>
    //可迭代类自己实现迭代器
{
    private T[] _data;

    private int _currentIdex;
    
    public T Current => this[_currentIdex];

    object IEnumerator.Current => Current;

    public T this[int index]
    {
        get
        {
            return _data[index];
        }
        set
        {
            _data[index] = value;
        }
    }
    public MyIEnumerableClass(T[] data)
    {
        _data = data;
        _currentIdex = -1;
    }
    
    public IEnumerator<T> GetEnumerator()
    {
        return this;
    }
    
    IEnumerator IEnumerable.GetEnumerator()
    {
        return this.GetEnumerator();
    }
    
    public bool MoveNext()
    {
        if (_currentIdex < _data.Length-1)
            _currentIdex++;
        else
            return false;
        return true;
    }
    
    public void Reset()
    {
        _currentIdex = 0;
    }
    
    public void Dispose()
    {
    }
}

IEnumerable接口调用GetEnumerator()方法视是否为泛型而定,返回一个枚举器IEnumerator（可以自己实现，或者用yield return语句，编译器会自己实现）。在foreach语句中，先调用类中的GetEnumerator()方法，生成枚举器，然后循环调用MoveNext()判断bool值，使用用Current执行foreach中的语句。

foreach调用迭代器，但迭代器一旦生成后无法修改迭代类。如果要修改只能用for循环，并调用linq中的ElementAt方法。

for (int j = start; j < keyValues.Count; j++)
        {
            item = keyValues.ElementAt(j).Key;
            if (keyValues[item] == 0)
                continue;
            var i = sum - item;
            if (i < item)
                break;
            tempset.Add(item);
            keyValues[item]--;
            dfs(returnSet, i, keyValues, tempset,j);
            keyValues[item]++;
            tempset.Remove(item);
        }

2. yield return ,yield break

用yield实现迭代。

public class YieldReturnEnumerableClass<T> : IEnumerable<T>
{
    T[] _data;
    public YieldReturnEnumerableClass(T[] data)
    {
        _data = data;
    }
    public IEnumerator<T> GetEnumerator()
    {
        int i = 0;
        while(true)
        {
            if (i == _data.Length)
                yield break;
            yield return _data[i];
            i++;
        }
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return this.GetEnumerator();
    }
}

yield只能用在IEnumerable,IEnumerator代码块中。
实现交替输出上下操作。

public class MoveGame
{
    IEnumerator _moveUp;
    IEnumerator _moveDown;
    int count;
    int maxStep;
    public MoveGame(int max)
    {
        maxStep = max;
        _moveDown = moveDown();
        _moveUp = moveUp();
        count = 0;
    }
    public IEnumerator moveUp()
    {
        while (true)
        {
            Console.WriteLine("move up:{0}", count);
            count++;
            if (count < maxStep)
                yield return _moveDown;
            else
                yield break;
        }
    }
    public IEnumerator moveDown()
    {
        while (true)
        {
            Console.WriteLine("move up:{0}", count);
            count++;
            if (count < maxStep)
                yield return _moveUp;
            else
                yield break;
        }
    }
}
class Program
{
    static void Main(string[] args)
    {
        MoveGame move = new MoveGame(10);
        IEnumerator ie = move.moveUp();
        while (ie.MoveNext())
            ie = ie.Current as IEnumerator;
    }
}

3. ICollection

Properties

Methods

4. IList

Properties

Methods

5. IDisposable

class BaseClass : IDisposable
{
   // Flag: Has Dispose already been called?
   bool disposed = false;

   // Public implementation of Dispose pattern callable by consumers.
   public void Dispose()
   {
      Dispose(disposing: true);
      GC.SuppressFinalize(this);
   }

   // Protected implementation of Dispose pattern.
   protected virtual void Dispose(bool disposing)
   {
      if (disposed)
         return;

      if (disposing) {
         // Free any other managed objects here.
         //
      }

      // Free any unmanaged objects here.
      //
      disposed = true;
   }

   ~BaseClass()
   {
      Dispose(disposing: false);
   }
}

void Dispose()中调用一个线程安全的Dispose方法（通过信号量disposed），并且由于实现了Dispose接口后GC不会主动释放类，还需要实现对GC的调用

6. ISet

每个元素独一无二

7. IDictionary

8. ICompare

Compare(Object, Object)实现比较方法

9. IEqualityComparer

Equals(T, T)该方法与一般语义下的Equals相同
GetHashCode(T)自定义hashcode

10. ILookup

查询

public static void ILookupExample()
{
    // Create a list of Packages to put into an ILookup data structure.
    List<Package> packages = new List<Package> { new Package { Company = "Coho Vineyard", Weight = 25.2, TrackingNumber = 89453312L },
                                                 new Package { Company = "Lucerne Publishing", Weight = 18.7, TrackingNumber = 89112755L },
                                                 new Package { Company = "Wingtip Toys", Weight = 6.0, TrackingNumber = 299456122L },
                                                 new Package { Company = "Contoso Pharmaceuticals", Weight = 9.3, TrackingNumber = 670053128L },
                                                 new Package { Company = "Wide World Importers", Weight = 33.8, TrackingNumber = 4665518773L } };

// Create a Lookup to organize the packages. Use the first character of Company as the key value.
// Select Company appended to TrackingNumber for each element value in the ILookup object.
ILookup<char, string> packageLookup = packages.ToLookup(
    p => Convert.ToChar(p.Company.Substring(0, 1)),
    p => p.Company + " " + p.TrackingNumber
    );

// Iterate through each value in the ILookup and output the contents.
foreach (var packageGroup in packageLookup)
{
    // Print the key value.
    Console.WriteLine(packageGroup.Key);
    // Iterate through each value in the collection.
    foreach (string str in packageGroup)
        Console.WriteLine("    {0}", str);
}

// This code produces the following output:
//
// C
//     Coho Vineyard 89453312
//     Contoso Pharmaceuticals 670053128
// L
//     Lucerne Publishing 89112755
// W
//     Wingtip Toys 299456122
//     Wide World Importers 4665518773

}

常用接口