Add OrderedDictionary

src/libraries/Common/src/System/Collections/Generic/EnumerableHelpers.cs

@@ -8,6 +8,10 @@ namespace System.Collections.Generic
  /// </summary>
  internal static partial class EnumerableHelpers
  {
+ /// <summary>Calls Reset on an enumerator instance.</summary>
+ /// <remarks>Enables Reset to be called without boxing on a struct enumerator that lacks a public Reset.</remarks>
+ internal static void Reset<T>(ref T enumerator) where T : IEnumerator => enumerator.Reset();
+
  /// <summary>Gets an enumerator singleton for an empty collection.</summary>
  internal static IEnumerator<T> GetEmptyEnumerator<T>() =>
  ((IEnumerable<T>)Array.Empty<T>()).GetEnumerator();

src/libraries/Common/tests/System/Collections/IDictionary.NonGeneric.Tests.cs

@@ -491,7 +491,6 @@ public virtual void IDictionary_NonGeneric_Values_Enumeration_ParentDictionaryMo
  {
  Assert.Throws<InvalidOperationException>(() => valuesEnum.MoveNext());
  Assert.Throws<InvalidOperationException>(() => valuesEnum.Reset());
- Assert.Throws<InvalidOperationException>(() => valuesEnum.Current);
  }
  else
  {
@@ -832,7 +831,7 @@ public virtual void IDictionary_NonGeneric_IDictionaryEnumerator_Current_AfterEn
  object current, key, value, entry;
  IDictionaryEnumerator enumerator = NonGenericIDictionaryFactory(count).GetEnumerator();
  while (enumerator.MoveNext()) ;
- if (Enumerator_Current_UndefinedOperation_Throws)
+ if (count == 0 ? Enumerator_Empty_Current_UndefinedOperation_Throw : Enumerator_Current_UndefinedOperation_Throws)
  {
  Assert.Throws<InvalidOperationException>(() => enumerator.Current);
  Assert.Throws<InvalidOperationException>(() => enumerator.Key);

src/libraries/Common/tests/System/Collections/IEnumerable.NonGeneric.Tests.cs

@@ -60,6 +60,18 @@ public abstract partial class IEnumerable_NonGeneric_Tests : TestBase
  /// </summary>
  protected virtual bool Enumerator_Current_UndefinedOperation_Throws => false;
 
+ /// <summary>
+ /// When calling Current of the empty enumerator before the first MoveNext, after the end of the collection,
+ /// or after modification of the enumeration, the resulting behavior is undefined. Tests are included
+ /// to cover two behavioral scenarios:
+ /// - Throwing an InvalidOperationException
+ /// - Returning an undefined value.
+ ///
+ /// If this property is set to true, the tests ensure that the exception is thrown. The default value is
+ /// false.
+ /// </summary>
+ protected virtual bool Enumerator_Empty_Current_UndefinedOperation_Throw => Enumerator_Current_UndefinedOperation_Throws;
+
  /// <summary>
  /// When calling MoveNext or Reset after modification of the enumeration, the resulting behavior is
  /// undefined. Tests are included to cover two behavioral scenarios:
@@ -305,7 +317,7 @@ public virtual void Enumerator_Current_BeforeFirstMoveNext_UndefinedBehavior(int
  object current;
  IEnumerable enumerable = NonGenericIEnumerableFactory(count);
  IEnumerator enumerator = enumerable.GetEnumerator();
- if (Enumerator_Current_UndefinedOperation_Throws)
+ if (count == 0 ? Enumerator_Empty_Current_UndefinedOperation_Throw : Enumerator_Current_UndefinedOperation_Throws)
  Assert.Throws<InvalidOperationException>(() => enumerator.Current);
  else
  current = enumerator.Current;
@@ -319,7 +331,7 @@ public virtual void Enumerator_Current_AfterEndOfEnumerable_UndefinedBehavior(in
  IEnumerable enumerable = NonGenericIEnumerableFactory(count);
  IEnumerator enumerator = enumerable.GetEnumerator();
  while (enumerator.MoveNext()) ;
- if (Enumerator_Current_UndefinedOperation_Throws)
+ if (count == 0 ? Enumerator_Empty_Current_UndefinedOperation_Throw : Enumerator_Current_UndefinedOperation_Throws)
  Assert.Throws<InvalidOperationException>(() => enumerator.Current);
  else
  current = enumerator.Current;
@@ -336,7 +348,7 @@ public virtual void Enumerator_Current_ModifiedDuringEnumeration_UndefinedBehavi
  IEnumerator enumerator = enumerable.GetEnumerator();
  if (ModifyEnumerable(enumerable))
  {
- if (Enumerator_Current_UndefinedOperation_Throws)
+ if (count == 0 ? Enumerator_Empty_Current_UndefinedOperation_Throw : Enumerator_Current_UndefinedOperation_Throws)
  Assert.Throws<InvalidOperationException>(() => enumerator.Current);
  else
  current = enumerator.Current;

src/libraries/Common/tests/System/Collections/IList.Generic.Tests.cs

@@ -103,17 +103,31 @@ protected override IEnumerable<ModifyEnumerable> GetModifyEnumerables(ModifyOper
  public void IList_Generic_ItemGet_NegativeIndex_ThrowsException(int count)
  {
  IList<T> list = GenericIListFactory(count);
+
  Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => list[-1]);
  Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => list[int.MinValue]);
+
+ if (list is IReadOnlyList<T> rol)
+ {
+ Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => rol[-1]);
+ Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => rol[int.MinValue]);
+ }
  }
 
  [Theory]
  [MemberData(nameof(ValidCollectionSizes))]
  public void IList_Generic_ItemGet_IndexGreaterThanListCount_ThrowsException(int count)
  {
  IList<T> list = GenericIListFactory(count);
+
  Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => list[count]);
  Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => list[count + 1]);
+
+ if (list is IReadOnlyList<T> rol)
+ {
+ Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => rol[count]);
+ Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => rol[count + 1]);
+ }
  }
 
  [Theory]
@@ -122,7 +136,15 @@ public void IList_Generic_ItemGet_ValidGetWithinListBounds(int count)
  {
  IList<T> list = GenericIListFactory(count);
  T result;
+
  Assert.All(Enumerable.Range(0, count), index => result = list[index]);
+ Assert.All(Enumerable.Range(0, count), index => Assert.Equal(list[index], list[index]));
+
+ if (list is IReadOnlyList<T> rol)
+ {
+ Assert.All(Enumerable.Range(0, count), index => result = rol[index]);
+ Assert.All(Enumerable.Range(0, count), index => Assert.Equal(rol[index], rol[index]));
+ }
  }
 
  #endregion
@@ -369,7 +391,7 @@ public void IList_Generic_IndexOf_InvalidValue(int count)
  [MemberData(nameof(ValidCollectionSizes))]
  public void IList_Generic_IndexOf_ReturnsFirstMatchingValue(int count)
  {
- if (!IsReadOnly && !AddRemoveClear_ThrowsNotSupported)
+ if (!IsReadOnly && !AddRemoveClear_ThrowsNotSupported && DuplicateValuesAllowed)
  {
  IList<T> list = GenericIListFactory(count);
  foreach (T duplicate in list.ToList()) // hard copies list to circumvent enumeration error

src/libraries/Common/tests/System/Collections/IList.NonGeneric.Tests.cs

@@ -83,6 +83,17 @@ protected virtual object CreateT(int seed)
  /// </summary>
  protected virtual bool IList_CurrentAfterAdd_Throws => Enumerator_Current_UndefinedOperation_Throws;
 
+ /// <summary>
+ /// When calling Current of the empty enumerator after the end of the list and list is extended by new items.
+ /// Tests are included to cover two behavioral scenarios:
+ /// - Throwing an InvalidOperationException
+ /// - Returning an undefined value.
+ ///
+ /// If this property is set to true, the tests ensure that the exception is thrown. The default value is
+ /// the same as Enumerator_Current_UndefinedOperation_Throws.
+ /// </summary>
+ protected virtual bool IList_Empty_CurrentAfterAdd_Throws => Enumerator_Empty_Current_UndefinedOperation_Throw;
+
  #endregion
 
  #region ICollection Helper Methods
@@ -697,7 +708,7 @@ public void IList_NonGeneric_IndexOf_InvalidValue(int count)
  [MemberData(nameof(ValidCollectionSizes))]
  public void IList_NonGeneric_IndexOf_ReturnsFirstMatchingValue(int count)
  {
- if (!IsReadOnly && !ExpectedFixedSize)
+ if (!IsReadOnly && !ExpectedFixedSize && DuplicateValuesAllowed)
  {
  IList list = NonGenericIListFactory(count);
 
@@ -1084,7 +1095,7 @@ public void IList_NonGeneric_CurrentAtEnd_AfterAdd(int count)
  IEnumerator enumerator = collection.GetEnumerator();
  while (enumerator.MoveNext()) ; // Go to end of enumerator
 
- if (Enumerator_Current_UndefinedOperation_Throws)
+ if (count == 0 ? Enumerator_Empty_Current_UndefinedOperation_Throw : Enumerator_Current_UndefinedOperation_Throws)
  {
  Assert.Throws<InvalidOperationException>(() => enumerator.Current); // Enumerator.Current should fail
  }
@@ -1099,7 +1110,7 @@ public void IList_NonGeneric_CurrentAtEnd_AfterAdd(int count)
  {
  collection.Add(CreateT(seed++));
 
- if (IList_CurrentAfterAdd_Throws)
+ if (count == 0 ? IList_Empty_CurrentAfterAdd_Throws : IList_CurrentAfterAdd_Throws)
  {
  Assert.Throws<InvalidOperationException>(() => enumerator.Current); // Enumerator.Current should fail
  }