Implement dotnet#28776: LINQ APIs for index and range. Code review up…

…date.
Dixin · Feb 7, 2021 · 52b8617 · 52b8617
1 parent e9922bf
commit 52b8617
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Showing 2 changed files with 8 additions and 19 deletions.
diff --git a/src/libraries/System.Linq/src/System/Linq/ElementAt.cs b/src/libraries/System.Linq/src/System/Linq/ElementAt.cs
@@ -74,13 +74,12 @@ public static TSource ElementAt<TSource>(this IEnumerable<TSource> source, Index
                 return source.ElementAt(index.Value);
             }
 
-            if (TryGetElementAt(source, index.Value, out TSource? result))
+            if (!TryGetElementAt(source, index.Value, out TSource? result))
             {
-                return result;
+                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index);
             }
 
-            ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index);
-            return default;
+            return result!;
         }
 
         public static TSource? ElementAtOrDefault<TSource>(this IEnumerable<TSource> source, int index)
@@ -150,7 +149,7 @@ public static TSource ElementAt<TSource>(this IEnumerable<TSource> source, Index
             return result;
         }
 
-        private static bool TryGetElementAt<TSource>(IEnumerable<TSource> source, int indexFromEnd, [NotNullWhen(true)] out TSource? result)
+        private static bool TryGetElementAt<TSource>(IEnumerable<TSource> source, int indexFromEnd, [MaybeNullWhen(false)] out TSource? result)
         {
             Debug.Assert(indexFromEnd >= 0);
 
@@ -184,7 +183,7 @@ private static bool TryGetElementAt<TSource>(IEnumerable<TSource> source, int in
                 int count = list.Count;
                 if (indexFromEnd <= count)
                 {
-                    result = list[count - indexFromEnd]!;
+                    result = list[count - indexFromEnd];
                     return true;
                 }
 
@@ -211,7 +210,7 @@ private static bool TryGetElementAt<TSource>(IEnumerable<TSource> source, int in
 
             if (queue.Count == indexFromEnd)
             {
-                result = queue.Dequeue()!;
+                result = queue.Dequeue();
                 return true;
             }
 

diff --git a/src/libraries/System.Linq/src/System/Linq/Take.cs b/src/libraries/System.Linq/src/System/Linq/Take.cs
@@ -46,7 +46,7 @@ public static IEnumerable<TSource> Take<TSource>(this IEnumerable<TSource> sourc
 
             if (isStartIndexFromEnd)
             {
-                if (startIndex == 0 || isEndIndexFromEnd && endIndex >= startIndex)
+                if (startIndex == 0 || (isEndIndexFromEnd && endIndex >= startIndex))
                 {
                     return Empty<TSource>();
                 }
@@ -123,13 +123,8 @@ private static IEnumerable<TSource> TakeIterator<TSource>(
             }
             else
             {
-                if (!e.MoveNext())
-                {
-                    yield break;
-                }
-
                 int index = 0;
-                while (index < startIndex)
+                while (index <= startIndex)
                 {
                     if (!e.MoveNext())
                     {
@@ -142,11 +137,6 @@ private static IEnumerable<TSource> TakeIterator<TSource>(
                     }
                 }
 
-                if (index != startIndex)
-                {
-                    yield break;
-                }
-
                 if (isEndIndexFromEnd)
                 {
                     if (endIndex > 0)