Iterator.cs

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using System.Collections;
using System.Collections.Generic;
 
namespace System.IO;
 
internal abstract class Iterator<TSource> : IEnumerable<TSource>, IEnumerable, IEnumerator<TSource>, IDisposable, IEnumerator
{
    private readonly int _threadId;
 
    internal int state;
 
    internal TSource current;
 
    public TSource Current => current;
 
    object IEnumerator.Current => Current;
 
    public Iterator()
    {
        _threadId = Environment.CurrentManagedThreadId;
    }
 
    protected abstract Iterator<TSource> Clone();
 
    public void Dispose()
    {
        Dispose(disposing: true);
        GC.SuppressFinalize(this);
    }
 
    protected virtual void Dispose(bool disposing)
    {
        current = default(TSource);
        state = -1;
    }
 
    public IEnumerator<TSource> GetEnumerator()
    {
        if (state == 0 && _threadId == Environment.CurrentManagedThreadId)
        {
            state = 1;
            return this;
        }
        Iterator<TSource> iterator = Clone();
        iterator.state = 1;
        return iterator;
    }
 
    public abstract bool MoveNext();
 
    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
 
    void IEnumerator.Reset()
    {
        throw new NotSupportedException();
    }
}