支持 foreach 而不实现 IEnumerable 的示例

Question

我正在查看这个博客，其中解释了无需实施

foreach

即可支持

IEnumerable

。但不讨论实现的细节。

我正在寻找一个示例，说明如何在不实施

foreach

的情况下支持

IEnumerable

。

Answer 1

这是一个没有实现

IEnumerable

或任何接口的类：

public class Foo 
{
    public IEnumerator<int> GetEnumerator()
    {
        yield return 1;
        yield return 2;
    }
}

你可以像这样

foreach

：

foreach (int n in new Foo())
    Console.WriteLine(n);

这将打印：

1
2

Answer 2

感谢@Sam I am 的评论，我能够调整此页面上的代码并将以下内容放在一起，而无需使用 IEnumerable 或 IEnumerator：

   //Person Object
   public class Person
   {
        public Person(string fName, string lName)
        {
            this.firstName = fName;
            this.lastName = lName;
        }
    string firstName;
    public string lastName;
   }

   //****Object Collection. 
   //****This class usually needs to implement IEnumerable 
   //****But we are avoiding that here.
   public class People
   {
      private Person[] _people;
      public People(Person[] pArray)
        {
           _people = new Person[pArray.Length];    
           for (int i = 0; i < pArray.Length; i++)
           {
              _people[i] = pArray[i];
           }
         }

    public PeopleEnumSimulator GetEnumerator()
    {
        return new PeopleEnumSimulator(_people);
    }

    public class PeopleEnumSimulator
    {
        public Person[] _people;

        int position = -1;

        public PeopleEnumSimulator(Person[] list)
        {
            _people = list;
        }

        public bool MoveNext()
        {
            position++;
            return (position < _people.Length);
        }

        public void Reset()
        {
            position = -1;
        }

        public Person Current
        {
            get
            {
                try
                {
                    return _people[position];
                }
                catch (IndexOutOfRangeException)
                {
                    throw new InvalidOperationException();
                }
            }
        }
    }
}   


//****Now, Use the Foreach
    Person[] myPeople = new Person[3]
    {
        new Person("John", "Smith"),
        new Person("Jim", "Johnson"),
        new Person("Sue", "Rabon"),
    };
    People peopleList = new People(myPeople);
    foreach (Person p in peopleList)
        Response.Write(p.firstName + " " + p.lastName);





//****************************************
//******** A Generic Implementation********
public class People<T>
{
    private T[] _people;
    public People(T[] pArray)
    {
        _people = new T[pArray.Length];

        for (int i = 0; i < pArray.Length; i++)
        {
            _people[i] = pArray[i];
        }
    }

    public PeopleEnumSimulator GetEnumerator()
    {
        return new PeopleEnumSimulator(_people);
    }

    public class PeopleEnumSimulator
    {
        public T[] _people;

        int position = -1;

        public PeopleEnumSimulator(T[] list)
        {
            _people = list;
        }

        public bool MoveNext()
        {
            position++;
            return (position < _people.Length);
        }

        public void Reset()
        {
            position = -1;
        }

        public T Current
        {
            get
            {
                try
                {
                    return _people[position];
                }
                catch (IndexOutOfRangeException)
                {
                    throw new InvalidOperationException();
                }
            }
        }
    }
}

       // use the foreach
       //For Type Person
            People<Person> peopleList = new People<Person>(myPeople);

            foreach (Person p in peopleList)
                Response.Write(p.firstName + " " + p.lastName);

            //break
            Response.Write(" </br></br></br>       ");

            //For Type Int
            int[] n3 = { 2, 4, 6, 8 };

            People<int> intList = new People<int>(n3);

            foreach (int p in intList)
                Response.Write(p);