With Java Iterators, I have used the hasNext method to determine whether an iteration has more elements (without consuming an element) -- thus, hasNext is like a "Peek" method.
My question: is there anything like a "hasNext" or "Peek" method with C#'s generic IEnumerators?
No, but in C# you can repeatedly ask for the current element without moving to the next one. It's just a different way of looking at it.
It wouldn't be too hard to write a C# class to take a .NET-style IEnumerator and return a Java-style Iterator. Personally I find the .NET style easier to use in most cases, but there we go :)
EDIT: Okay, this is completely untested, but I think it will work. It does at least compile :)
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();
}
}
No, unfortunately there isn't.
The IEnumerator<T> interface only exposes the following members:
Methods:
Dispose
MoveNext
Reset
Properties:
Current
You can also try having a look at this Implementing Peek to IEnumerator and IEnumerator<>. It's an extension method that adds the Peek functionality to IEnumerator. Hope it helps. :)
Use good old manual iteration
// 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
{
}
}
