通过反编译得到System.Core程序集中System.Linq命名空间下的Enumerable类如下所示:
using System.Collections; using System.Collections.Generic; using System.Threading; namespace System.Linq { [__DynamicallyInvokable] public static class Enumerable { private abstract class Iterator: IEnumerable , IEnumerable, IEnumerator , IDisposable, IEnumerator { private int threadId; internal int state; internal TSource current; public TSource Current => current; object IEnumerator.Current => Current; public Iterator() { threadId = Thread.CurrentThread.ManagedThreadId; } public abstract Iterator Clone(); public virtual void Dispose() { current = default(TSource); state = -1; } public IEnumerator GetEnumerator() { if (threadId == Thread.CurrentThread.ManagedThreadId && state == 0) { state = 1; return this; } Iterator iterator = Clone(); iterator.state = 1; return iterator; } public abstract bool MoveNext(); public abstract IEnumerable Select (Func selector); public abstract IEnumerable Where(Func bool> predicate); IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); } void IEnumerator.Reset() { throw new NotImplementedException(); } } private class WhereEnumerableIterator : Iterator { private IEnumerable source; private Func bool> predicate; private IEnumerator enumerator; public WhereEnumerableIterator(IEnumerable source, Func bool> predicate) { this.source = source; this.predicate = predicate; } public override Iterator Clone() { return new WhereEnumerableIterator (source, predicate); } public override void Dispose() { if (enumerator != null) { enumerator.Dispose(); } enumerator = null; base.Dispose(); } public override bool MoveNext() { int state = base.state; if (state != 1) { if (state != 2) { goto IL_0061; } } else { enumerator = source.GetEnumerator(); base.state = 2; } while (enumerator.MoveNext()) { TSource current = enumerator.Current; if (predicate(current)) { base.current = current; return true; } } Dispose(); goto IL_0061; IL_0061: return false; } public override IEnumerable Select (Func selector) { return new WhereSelectEnumerableIterator (source, predicate, selector); } public override IEnumerable Where(Func bool> predicate) { return new WhereEnumerableIterator (source, CombinePredicates(this.predicate, predicate)); } } private class WhereArrayIterator : Iterator { private TSource[] source; private Func bool> predicate; private int index; public WhereArrayIterator(TSource[] source, Func bool> predicate) { this.source = source; this.predicate = predicate; } public override Iterator Clone() { return new WhereArrayIterator (source, predicate); } public override bool MoveNext() { if (state == 1) { while (index < source.Length) { TSource val = source[index]; index++; if (predicate(val)) { current = val; return true; } } Dispose(); } return false; } public override IEnumerable Select (Func selector) { return new WhereSelectArrayIterator (source, predicate, selector); } public override IEnumerable Where(Func bool> predicate) { return new WhereArrayIterator (source, CombinePredicates(this.predicate, predicate)); } } private class WhereListIterator : Iterator { private List source; private Func bool> predicate; private List .Enumerator enumerator; public WhereListIterator(List source, Func bool> predicate) { this.source = source; this.predicate = predicate; } public override Iterator Clone() { return new WhereListIterator (source, predicate); } public override bool MoveNext() { int state = base.state; if (state != 1) { if (state != 2) { goto IL_0061; } } else { enumerator = source.GetEnumerator(); base.state = 2; } while (enumerator.MoveNext()) { TSource current = enumerator.Current; if (predicate(current)) { base.current = current; return true; } } Dispose(); goto IL_0061; IL_0061: return false; } public override IEnumerable Select (Func selector) { return new WhereSelectListIterator (source, predicate, selector); } public override IEnumerable Where(Func bool> predicate) { return new WhereListIterator (source, CombinePredicates(this.predicate, predicate)); } } private class SelectEnumerableIterator : Iterator , IIListProvider , IEnumerable , IEnumerable { private readonly IEnumerable _source; private readonly Func _selector; private IEnumerator _enumerator; public SelectEnumerableIterator(IEnumerable source, Func selector) { _source = source; _selector = selector; } public override Iterator Clone() { return new SelectEnumerableIterator (_source, _selector); } public override void Dispose() { if (_enumerator != null) { _enumerator.Dispose(); _enumerator = null; } base.Dispose(); } public override bool MoveNext() { int state = base.state; if (state != 1) { if (state != 2) { goto IL_005a; } } else { _enumerator = _source.GetEnumerator(); base.state = 2; } if (_enumerator.MoveNext()) { current = _selector(_enumerator.Current); return true; } Dispose(); goto IL_005a; IL_005a: return false; } public override IEnumerable Select (Func selector) { return new SelectEnumerableIterator (_source, CombineSelectors(_selector, selector)); } public override IEnumerable Where(Func bool> predicate) { return new WhereEnumerableIterator (this, predicate); } public TResult[] ToArray() { LargeArrayBuilder largeArrayBuilder = new LargeArrayBuilder (initialize: true); foreach (TSource item in _source) { largeArrayBuilder.Add(_selector(item)); } return largeArrayBuilder.ToArray(); } public List ToList() { List list = new List (); foreach (TSource item in _source) { list.Add(_selector(item)); } return list; } public int GetCount(bool onlyIfCheap) { if (onlyIfCheap) { return -1; } int num = 0; foreach (TSource item in _source) { _selector(item); num = checked(num + 1); } return num; } } private class WhereSelectEnumerableIterator : Iterator { private IEnumerable source; private Func bool> predicate; private Func selector; private IEnumerator enumerator; public WhereSelectEnumerableIterator(IEnumerable source, Func bool> predicate, Func selector) { this.source = source; this.predicate = predicate; this.selector = selector; } public override Iterator Clone() { return new WhereSelectEnumerableIterator (source, predicate, selector); } public override void Dispose() { if (enumerator != null) { enumerator.Dispose(); } enumerator = null; base.Dispose(); } public override bool MoveNext() { int state = base.state; if (state != 1) { if (state != 2) { goto IL_0074; } } else { enumerator = source.GetEnumerator(); base.state = 2; } while (enumerator.MoveNext()) { TSource current = enumerator.Current; if (predicate == null || predicate(current)) { base.current = selector(current); return true; } } Dispose(); goto IL_0074; IL_0074: return false; } public override IEnumerable Select (Func selector) { return new WhereSelectEnumerableIterator (source, predicate, CombineSelectors(this.selector, selector)); } public override IEnumerable Where(Func bool> predicate) { return new WhereEnumerableIterator (this, predicate); } } private class WhereSelectArrayIterator : Iterator { private TSource[] source; private Func bool> predicate; private Func selector; private int index; public WhereSelectArrayIterator(TSource[] source, Func bool> predicate, Func selector) { this.source = source; this.predicate = predicate; this.selector = selector; } public override Iterator Clone() { return new WhereSelectArrayIterator (source, predicate, selector); } public override bool MoveNext() { if (state == 1) { while (index < source.Length) { TSource arg = source[index]; index++; if (predicate == null || predicate(arg)) { current = selector(arg); return true; } } Dispose(); } return false; } public override IEnumerable Select (Func selector) { return new WhereSelectArrayIterator (source, predicate, CombineSelectors(this.selector, selector)); } public override IEnumerable Where(Func bool> predicate) { return new WhereEnumerableIterator (this, predicate); } } private class WhereSelectListIterator : Iterator { private List source; private Func bool> predicate; private Func selector; private List .Enumerator enumerator; public WhereSelectListIterator(List source, Func bool> predicate, Func selector) { this.source = source; this.predicate = predicate; this.selector = selector; } public override Iterator Clone() { return new WhereSelectListIterator (source, predicate, selector); } public override bool MoveNext() { int state = base.state; if (state != 1) { if (state != 2) { goto IL_0074; } } else { enumerator = source.GetEnumerator(); base.state = 2; } while (enumerator.MoveNext()) { TSource current = enumerator.Current; if (predicate == null || predicate(current)) { base.current = selector(current); return true; } } Dispose(); goto IL_0074; IL_0074: return false; } public override IEnumerable Select (Func selector) { return new WhereSelectListIterator (source, predicate, CombineSelectors(this.selector, selector)); } public override IEnumerable Where(Func bool> predicate) { return new WhereEnumerableIterator (this, predicate); } } private abstract class AppendPrependIterator : Iterator , IIListProvider , IEnumerable , IEnumerable { protected readonly IEnumerable _source; protected IEnumerator enumerator; protected AppendPrependIterator(IEnumerable source) { _source = source; } protected void GetSourceEnumerator() { enumerator = _source.GetEnumerator(); } public abstract AppendPrependIterator Append(TSource item); public abstract AppendPrependIterator Prepend(TSource item); protected bool LoadFromEnumerator() { if (enumerator.MoveNext()) { current = enumerator.Current; return true; } Dispose(); return false; } public override void Dispose() { if (enumerator != null) { enumerator.Dispose(); enumerator = null; } base.Dispose(); } public override IEnumerable Select (Func selector) { return new SelectEnumerableIterator (this, selector); } public override IEnumerable Where(Func bool> predicate) { return new WhereEnumerableIterator (this, predicate); } public abstract TSource[] ToArray(); public abstract List ToList(); public abstract int GetCount(bool onlyIfCheap); } private class AppendPrepend1Iterator : AppendPrependIterator { private readonly TSource _item; private readonly bool _appending; public AppendPrepend1Iterator(IEnumerable source, TSource item, bool appending) : base(source) { _item = item; _appending = appending; } public override Iterator Clone() { return new AppendPrepend1Iterator (_source, _item, _appending); } public override bool MoveNext() { switch (state) { case 1: state = 2; if (!_appending) { current = _item; return true; } goto case 2; case 2: GetSourceEnumerator(); state = 3; goto case 3; case 3: if (LoadFromEnumerator()) { return true; } if (_appending) { current = _item; return true; } break; } Dispose(); return false; } public override AppendPrependIterator Append(TSource item) { if (_appending) { return new AppendPrependN (_source, null, new SingleLinkedNode (_item).Add(item), 0, 2); } return new AppendPrependN (_source, new SingleLinkedNode (_item), new SingleLinkedNode (item), 1, 1); } public override AppendPrependIterator Prepend(TSource item) { if (_appending) { return new AppendPrependN (_source, new SingleLinkedNode (item), new SingleLinkedNode (_item), 1, 1); } return new AppendPrependN (_source, new SingleLinkedNode (_item).Add(item), null, 2, 0); } private TSource[] LazyToArray() { LargeArrayBuilder largeArrayBuilder = new LargeArrayBuilder (initialize: true); if (!_appending) { largeArrayBuilder.SlowAdd(_item); } largeArrayBuilder.AddRange(_source); if (_appending) { largeArrayBuilder.SlowAdd(_item); } return largeArrayBuilder.ToArray(); } public override TSource[] ToArray() { int count = GetCount(onlyIfCheap: true); if (count == -1) { return LazyToArray(); } TSource[] array = new TSource[count]; int arrayIndex; if (_appending) { arrayIndex = 0; } else { array[0] = _item; arrayIndex = 1; } EnumerableHelpers.Copy(_source, array, arrayIndex, count - 1); if (_appending) { array[array.Length - 1] = _item; } return array; } public override List ToList() { int count = GetCount(onlyIfCheap: true); List list = (count == -1) ? new List () : new List (count); if (!_appending) { list.Add(_item); } list.AddRange(_source); if (_appending) { list.Add(_item); } return list; } public override int GetCount(bool onlyIfCheap) { IIListProvider iIListProvider = _source as IIListProvider ; if (iIListProvider != null) { int count = iIListProvider.GetCount(onlyIfCheap); if (count != -1) { return count + 1; } return -1; } if (onlyIfCheap && !(_source is ICollection )) { return -1; } return _source.Count() + 1; } } private class AppendPrependN : AppendPrependIterator { private readonly SingleLinkedNode _prepended; private readonly SingleLinkedNode _appended; private readonly int _prependCount; private readonly int _appendCount; private SingleLinkedNode _node; public AppendPrependN(IEnumerable source, SingleLinkedNode prepended, SingleLinkedNode appended, int prependCount, int appendCount) : base(source) { _prepended = prepended; _appended = appended; _prependCount = prependCount; _appendCount = appendCount; } public override Iterator Clone() { return new AppendPrependN (_source, _prepended, _appended, _prependCount, _appendCount); } public override bool MoveNext() { switch (state) { case 1: _node = _prepended; state = 2; goto case 2; case 2: if (_node != null) { current = _node.Item; _node = _node.Linked; return true; } GetSourceEnumerator(); state = 3; goto case 3; case 3: if (LoadFromEnumerator()) { return true; } if (_appended == null) { return false; } enumerator = _appended.GetEnumerator(_appendCount); state = 4; goto case 4; case 4: return LoadFromEnumerator(); default: Dispose(); return false; } } public override AppendPrependIterator Append(TSource item) { SingleLinkedNode appended = (_appended != null) ? _appended.Add(item) : new SingleLinkedNode (item); return new AppendPrependN (_source, _prepended, appended, _prependCount, _appendCount + 1); } public override AppendPrependIterator Prepend(TSource item) { SingleLinkedNode prepended = (_prepended != null) ? _prepended.Add(item) : new SingleLinkedNode (item); return new AppendPrependN (_source, prepended, _appended, _prependCount + 1, _appendCount); } private TSource[] LazyToArray() { SparseArrayBuilder sparseArrayBuilder = new SparseArrayBuilder (initialize: true); if (_prepended != null) { sparseArrayBuilder.Reserve(_prependCount); } sparseArrayBuilder.AddRange(_source); if (_appended != null) { sparseArrayBuilder.Reserve(_appendCount); } TSource[] array = sparseArrayBuilder.ToArray(); int num = 0; for (SingleLinkedNode singleLinkedNode = _prepended; singleLinkedNode != null; singleLinkedNode = singleLinkedNode.Linked) { array[num++] = singleLinkedNode.Item; } num = array.Length - 1; for (SingleLinkedNode singleLinkedNode2 = _appended; singleLinkedNode2 != null; singleLinkedNode2 = singleLinkedNode2.Linked) { array[num--] = singleLinkedNode2.Item; } return array; } public override TSource[] ToArray() { int count = GetCount(onlyIfCheap: true); if (count == -1) { return LazyToArray(); } TSource[] array = new TSource[count]; int num = 0; for (SingleLinkedNode singleLinkedNode = _prepended; singleLinkedNode != null; singleLinkedNode = singleLinkedNode.Linked) { array[num] = singleLinkedNode.Item; num++; } ICollection collection = _source as ICollection ; if (collection != null) { collection.CopyTo(array, num); } else { foreach (TSource item in _source) { TSource val = array[num] = item; num++; } } num = array.Length; for (SingleLinkedNode singleLinkedNode2 = _appended; singleLinkedNode2 != null; singleLinkedNode2 = singleLinkedNode2.Linked) { num--; array[num] = singleLinkedNode2.Item; } return array; } public override List ToList() { int count = GetCount(onlyIfCheap: true); List list = (count == -1) ? new List () : new List (count); for (SingleLinkedNode singleLinkedNode = _prepended; singleLinkedNode != null; singleLinkedNode = singleLinkedNode.Linked) { list.Add(singleLinkedNode.Item); } list.AddRange(_source); if (_appended != null) { IEnumerator enumerator = _appended.GetEnumerator(_appendCount); while (enumerator.MoveNext()) { list.Add(enumerator.Current); } } return list; } public override int GetCount(bool onlyIfCheap) { IIListProvider iIListProvider = _source as IIListProvider ; if (iIListProvider != null) { int count = iIListProvider.GetCount(onlyIfCheap); if (count != -1) { return count + _appendCount + _prependCount; } return -1; } if (onlyIfCheap && !(_source is ICollection )) { return -1; } return _source.Count() + _appendCount + _prependCount; } } [__DynamicallyInvokable] public static IEnumerable Where (this IEnumerable source, Func bool> predicate) { if (source == null) { throw Error.ArgumentNull("source"); } if (predicate == null) { throw Error.ArgumentNull("predicate"); } if (source is Iterator ) { return ((Iterator )source).Where(predicate); } if (source is TSource[]) { return new WhereArrayIterator ((TSource[])source, predicate); } if (source is List ) { return new WhereListIterator ((List )source, predicate); } return new WhereEnumerableIterator (source, predicate); } [__DynamicallyInvokable] public static IEnumerable Where (this IEnumerable source, Func int, bool> predicate) { if (source == null) { throw Error.ArgumentNull("source"); } if (predicate == null) { throw Error.ArgumentNull("predicate"); } return WhereIterator(source, predicate); } private static IEnumerable WhereIterator (IEnumerable source, Func int, bool> predicate) { int index = -1; foreach (TSource item in source) { index = checked(index + 1); if (predicate(item, index)) { yield return item; } } } [__DynamicallyInvokable] public static IEnumerable Select (this IEnumerable source, Func selector) { if (source == null) { throw Error.ArgumentNull("source"); } if (selector == null) { throw Error.ArgumentNull("selector"); } if (source is Iterator ) { return ((Iterator )source).Select(selector); } if (source is TSource[]) { return new WhereSelectArrayIterator ((TSource[])source, null, selector); } if (source is List ) { return new WhereSelectListIterator ((List )source, null, selector); } return new WhereSelectEnumerableIterator (source, null, selector); } [__DynamicallyInvokable] public static IEnumerable Select (this IEnumerable source, Func int, TResult> selector) { if (source == null) { throw Error.ArgumentNull("source"); } if (selector == null) { throw Error.ArgumentNull("selector"); } return SelectIterator(source, selector); } private static IEnumerable SelectIterator (IEnumerable source, Func