Make it easier to iterate through an ArraySegment (dotnet/coreclr#8559)

* Make it easier to iterate through an ArraySegment. See Make it easier to iterate through an ArraySegment Commit migrated from dotnet/coreclr@2813ef4
picenka21 · Dec 9, 2016 · c33e26b · c33e26b
1 parent d9df14c
commit c33e26b
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Showing 2 changed files with 40 additions and 39 deletions.
diff --git a/src/coreclr/src/mscorlib/model.xml b/src/coreclr/src/mscorlib/model.xml
@@ -341,13 +341,21 @@
  <Member Name="get_Array" />
  <Member Name="get_Count" />
  <Member Name="get_Offset" />
+ <Member Name="GetEnumerator" />
  <Member Name="GetHashCode" />
  <Member Name="op_Equality(System.ArraySegment&lt;T&gt;,System.ArraySegment&lt;T&gt;)" />
  <Member Name="op_Inequality(System.ArraySegment&lt;T&gt;,System.ArraySegment&lt;T&gt;)" />
  <Member MemberType="Property" Name="Array" />
  <Member MemberType="Property" Name="Count" />
  <Member MemberType="Property" Name="Offset" />
  </Type>
+ <Type Name="System.ArraySegment&lt;T&gt;+Enumerator">
+ <Member Name="Dispose" />
+ <Member Name="get_Current" />
+ <Member Name="MoveNext" />
+ <Member MemberType="Property" Name="Current" />
+ <Member Name="System.Collections.IEnumerator.Reset" />
+ </Type>
  <Type Name="System.ArrayTypeMismatchException">
  <Member Name="#ctor" />
  <Member Name="#ctor(System.String)" />

diff --git a/src/coreclr/src/mscorlib/src/System/ArraySegment.cs b/src/coreclr/src/mscorlib/src/System/ArraySegment.cs
@@ -28,10 +28,10 @@ namespace System
  [Serializable]
  public struct ArraySegment<T> : IList<T>, IReadOnlyList<T>
  {
- private T[] _array;
- private int _offset;
- private int _count;
- 
+ private readonly T[] _array;
+ private readonly int _offset;
+ private readonly int _count;
+
  public ArraySegment(T[] array)
  {
  if (array == null)
@@ -67,7 +67,7 @@ public T[] Array
  Contract.Assert( (null == _array && 0 == _offset && 0 == _count)
  || (null != _array && _offset >= 0 && _count >= 0 && _offset + _count <= _array.Length),
  "ArraySegment is invalid");
- 
+
  return _array;
  }
  }
@@ -109,7 +109,16 @@ public int Count
  return _count;
  }
  }
-
+
+ public Enumerator GetEnumerator()
+ {
+ if (_array == null)
+ ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_NullArray);
+ Contract.EndContractBlock();
+
+ return new Enumerator(this);
+ }
+
  public override int GetHashCode()
  {
  if (_array == null)
@@ -184,7 +193,7 @@ int IList<T>.IndexOf(T item)
 
  int index = System.Array.IndexOf<T>(_array, item, _offset, _count);
 
- Contract.Assert(index == -1 || 
+ Contract.Assert(index == -1 ||
  (index >= _offset && index < _offset + _count));
 
  return index >= 0 ? index - _offset : -1;
@@ -269,46 +278,34 @@ bool ICollection<T>.Remove(T item)
  #endregion
 
  #region IEnumerable<T>
- IEnumerator<T> IEnumerable<T>.GetEnumerator()
- {
- if (_array == null)
- ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_NullArray);
- Contract.EndContractBlock();
 
- return new ArraySegmentEnumerator(this);
- }
+ IEnumerator<T> IEnumerable<T>.GetEnumerator() => GetEnumerator();
  #endregion
 
  #region IEnumerable
- IEnumerator IEnumerable.GetEnumerator()
- {
- if (_array == null)
- ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_NullArray);
- Contract.EndContractBlock();
 
- return new ArraySegmentEnumerator(this);
- }
+ IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
  #endregion
 
  [Serializable]
- private sealed class ArraySegmentEnumerator : IEnumerator<T>
+ public struct Enumerator : IEnumerator<T>
  {
- private T[] _array;
- private int _start;
- private int _end;
+ private readonly T[] _array;
+ private readonly int _start;
+ private readonly int _end; // cache Offset + Count, since it's a little slow
  private int _current;
 
- internal ArraySegmentEnumerator(ArraySegment<T> arraySegment)
+ internal Enumerator(ArraySegment<T> arraySegment)
  {
  Contract.Requires(arraySegment.Array != null);
  Contract.Requires(arraySegment.Offset >= 0);
  Contract.Requires(arraySegment.Count >= 0);
  Contract.Requires(arraySegment.Offset + arraySegment.Count <= arraySegment.Array.Length);
 
- _array = arraySegment._array;
- _start = arraySegment._offset;
- _end = _start + arraySegment._count;
- _current = _start - 1;
+ _array = arraySegment.Array;
+ _start = arraySegment.Offset;
+ _end = arraySegment.Offset + arraySegment.Count;
+ _current = arraySegment.Offset - 1;
  }
 
  public bool MoveNext()
@@ -325,19 +322,15 @@ public T Current
  {
  get
  {
- if (_current < _start) ThrowHelper.ThrowInvalidOperationException_InvalidOperation_EnumNotStarted();
- if (_current >= _end) ThrowHelper.ThrowInvalidOperationException_InvalidOperation_EnumEnded();
+ if (_current < _start)
+ ThrowHelper.ThrowInvalidOperationException_InvalidOperation_EnumNotStarted();
+ if (_current >= _end)
+ ThrowHelper.ThrowInvalidOperationException_InvalidOperation_EnumEnded();
  return _array[_current];
  }
  }
 
- object IEnumerator.Current
- {
- get
- {
- return Current;
- }
- }
+ object IEnumerator.Current => Current;
 
  void IEnumerator.Reset()
  {