在Java中,我使用Iterator
对象的hasNext
方法来判断迭代器是否还有更多元素(同时不会消耗元素),因此hasNext
方法就像一个"Peek
"方法。
我的问题是:C#的泛型IEnumerator
对象是否有类似于"hasNext
"或"Peek
"方法?
在Java中,我使用Iterator
对象的hasNext
方法来判断迭代器是否还有更多元素(同时不会消耗元素),因此hasNext
方法就像一个"Peek
"方法。
我的问题是:C#的泛型IEnumerator
对象是否有类似于"hasNext
"或"Peek
"方法?
using System;
using System.Collections;
using System.Collections.Generic;
// // Mimics Java's Iterable<T> interface
public interface IIterable<T>
{
IIterator<T> Iterator();
}
// Mimics Java's Iterator interface - but
// implements IDisposable for the sake of
// parity with IEnumerator.
public interface IIterator<T> : IDisposable
{
bool HasNext { get; }
T Next();
void Remove();
}
public sealed class EnumerableAdapter<T> : IIterable<T>
{
private readonly IEnumerable<T> enumerable;
public EnumerableAdapter(IEnumerable<T> enumerable)
{
this.enumerable = enumerable;
}
public IIterator<T> Iterator()
{
return new EnumeratorAdapter<T>(enumerable.GetEnumerator());
}
}
public sealed class EnumeratorAdapter<T> : IIterator<T>
{
private readonly IEnumerator<T> enumerator;
private bool fetchedNext = false;
private bool nextAvailable = false;
private T next;
public EnumeratorAdapter(IEnumerator<T> enumerator)
{
this.enumerator = enumerator;
}
public bool HasNext
{
get
{
CheckNext();
return nextAvailable;
}
}
public T Next()
{
CheckNext();
if (!nextAvailable)
{
throw new InvalidOperationException();
}
fetchedNext = false; // We've consumed this now
return next;
}
void CheckNext()
{
if (!fetchedNext)
{
nextAvailable = enumerator.MoveNext();
if (nextAvailable)
{
next = enumerator.Current;
}
fetchedNext = true;
}
}
public void Remove()
{
throw new NotSupportedException();
}
public void Dispose()
{
enumerator.Dispose();
}
}
public sealed class IterableAdapter<T> : IEnumerable<T>
{
private readonly IIterable<T> iterable;
public IterableAdapter(IIterable<T> iterable)
{
this.iterable = iterable;
}
public IEnumerator<T> GetEnumerator()
{
return new IteratorAdapter<T>(iterable.Iterator());
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
public sealed class IteratorAdapter<T> : IEnumerator<T>
{
private readonly IIterator<T> iterator;
private bool gotCurrent = false;
private T current;
public IteratorAdapter(IIterator<T> iterator)
{
this.iterator = iterator;
}
public T Current
{
get
{
if (!gotCurrent)
{
throw new InvalidOperationException();
}
return current;
}
}
object IEnumerator.Current
{
get { return Current; }
}
public bool MoveNext()
{
gotCurrent = iterator.HasNext;
if (gotCurrent)
{
current = iterator.Next();
}
return gotCurrent;
}
public void Reset()
{
throw new NotSupportedException();
}
public void Dispose()
{
iterator.Dispose();
}
}
枚举器通常是惰性评估的,因此HasNext几乎没有意义。
使用好老的手动迭代
// IEnumerable<>
for (int i = 0; i < enumerable.Count(); i++)
{
var item = enumerable.ElementAt(i);
if(i + 1 < enumerable.Count()) // eq. Iterator.HasNext
{
}
}
// IList<>
for (int i = 0; i < list.Count; i++)
{
var item = list[1];
if (i + 1 < list.Count) // eq. Iterator.HasNext
{
}
}