Merge pull request #1037 from dotnet/dev/bartde/switch_expr

Use C# 8.0 switch expression

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/Concat.cs

@@ -46,15 +46,12 @@ namespace System.Linq
 
             internal override IAsyncEnumerable<TSource>? GetAsyncEnumerable(int index)
             {
-                switch (index)
+                return index switch
                 {
-                    case 0:
-                        return _first;
-                    case 1:
-                        return _second;
-                    default:
-                        return null;
-                }
+                    0 => _first,
+                    1 => _second,
+                    _ => null,
+                };
             }
         }
 

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/Count.cs

@@ -16,17 +16,13 @@ namespace System.Linq
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
 
-            switch (source)
+            return source switch
             {
-                case ICollection<TSource> collection:
-                    return new ValueTask<int>(collection.Count);
-                case IAsyncIListProvider<TSource> listProv:
-                    return listProv.GetCountAsync(onlyIfCheap: false, cancellationToken);
-                case ICollection collection:
-                    return new ValueTask<int>(collection.Count);
-            }
-
-            return Core(source, cancellationToken);
+                ICollection<TSource> collection => new ValueTask<int>(collection.Count),
+                IAsyncIListProvider<TSource> listProv => listProv.GetCountAsync(onlyIfCheap: false, cancellationToken),
+                ICollection collection => new ValueTask<int>(collection.Count),
+                _ => Core(source, cancellationToken),
+            };
 
             static async ValueTask<int> Core(IAsyncEnumerable<TSource> source, CancellationToken cancellationToken)
             {

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/Select.cs

@@ -17,15 +17,12 @@ namespace System.Linq
             if (selector == null)
                 throw Error.ArgumentNull(nameof(selector));
 
-            switch (source)
+            return source switch
             {
-                case AsyncIterator<TSource> iterator:
-                    return iterator.Select(selector);
-                case IList<TSource> list:
-                    return new SelectIListIterator<TSource, TResult>(list, selector);
-            }
-
-            return new SelectEnumerableAsyncIterator<TSource, TResult>(source, selector);
+                AsyncIterator<TSource> iterator => iterator.Select(selector),
+                IList<TSource> list => new SelectIListIterator<TSource, TResult>(list, selector),
+                _ => new SelectEnumerableAsyncIterator<TSource, TResult>(source, selector),
+            };
         }
 
         public static IAsyncEnumerable<TResult> Select<TSource, TResult>(this IAsyncEnumerable<TSource> source, Func<TSource, int, TResult> selector)
@@ -60,15 +57,12 @@ namespace System.Linq
             if (selector == null)
                 throw Error.ArgumentNull(nameof(selector));
 
-            switch (source)
+            return source switch
             {
-                case AsyncIterator<TSource> iterator:
-                    return iterator.Select(selector);
-                case IList<TSource> list:
-                    return new SelectIListIteratorWithTask<TSource, TResult>(list, selector);
-            }
-
-            return new SelectEnumerableAsyncIteratorWithTask<TSource, TResult>(source, selector);
+                AsyncIterator<TSource> iterator => iterator.Select(selector),
+                IList<TSource> list => new SelectIListIteratorWithTask<TSource, TResult>(list, selector),
+                _ => new SelectEnumerableAsyncIteratorWithTask<TSource, TResult>(source, selector),
+            };
         }
 
 #if !NO_DEEP_CANCELLATION
@@ -79,15 +73,12 @@ namespace System.Linq
             if (selector == null)
                 throw Error.ArgumentNull(nameof(selector));
 
-            switch (source)
+            return source switch
             {
-                case AsyncIterator<TSource> iterator:
-                    return iterator.Select(selector);
-                case IList<TSource> list:
-                    return new SelectIListIteratorWithTaskAndCancellation<TSource, TResult>(list, selector);
-            }
-
-            return new SelectEnumerableAsyncIteratorWithTaskAndCancellation<TSource, TResult>(source, selector);
+                AsyncIterator<TSource> iterator => iterator.Select(selector),
+                IList<TSource> list => new SelectIListIteratorWithTaskAndCancellation<TSource, TResult>(list, selector),
+                _ => new SelectEnumerableAsyncIteratorWithTaskAndCancellation<TSource, TResult>(source, selector),
+            };
         }
 #endif
 

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/Single.cs

@@ -21,13 +21,12 @@ namespace System.Linq
             {
                 if (source is IList<TSource> list)
                 {
-                    switch (list.Count)
+                    return list.Count switch
                     {
-                        case 0: throw Error.NoElements();
-                        case 1: return list[0];
-                    }
-
-                    throw Error.MoreThanOneElement();
+                        0 => throw Error.NoElements(),
+                        1 => list[0],
+                        _ => throw Error.MoreThanOneElement(),
+                    };
                 }
 
                 await using var e = source.GetConfiguredAsyncEnumerator(cancellationToken, false);

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/SingleOrDefault.cs

@@ -21,13 +21,12 @@ namespace System.Linq
             {
                 if (source is IList<TSource> list)
                 {
-                    switch (list.Count)
+                    return list.Count switch
                     {
-                        case 0: return default!;
-                        case 1: return list[0];
-                    }
-
-                    throw Error.MoreThanOneElement();
+                        0 => default!,
+                        1 => list[0],
+                        _ => throw Error.MoreThanOneElement(),
+                    };
                 }
 
                 await using (var e = source.GetConfiguredAsyncEnumerator(cancellationToken, false))

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToAsyncEnumerable.cs

@@ -16,15 +16,12 @@ namespace System.Linq
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
 
-            switch (source)
+            return source switch
             {
-                case IList<TSource> list:
-                    return new AsyncIListEnumerableAdapter<TSource>(list);
-                case ICollection<TSource> collection:
-                    return new AsyncICollectionEnumerableAdapter<TSource>(collection);
-            }
-
-            return new AsyncEnumerableAdapter<TSource>(source);
+                IList<TSource> list => new AsyncIListEnumerableAdapter<TSource>(list),
+                ICollection<TSource> collection => new AsyncICollectionEnumerableAdapter<TSource>(collection),
+                _ => new AsyncEnumerableAdapter<TSource>(source),
+            };
         }
 
         private sealed class AsyncEnumerableAdapter<T> : AsyncIterator<T>, IAsyncIListProvider<T>

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/Union.cs

@@ -219,15 +219,13 @@ namespace System.Linq
             internal override IAsyncEnumerable<TSource>? GetEnumerable(int index)
             {
                 Debug.Assert(index >= 0 && index <= 2);
-                switch (index)
+
+                return index switch
                 {
-                    case 0:
-                        return _first;
-                    case 1:
-                        return _second;
-                    default:
-                        return null;
-                }
+                    0 => _first,
+                    1 => _second,
+                    _ => null,
+                };
             }
 
             internal override UnionAsyncIterator<TSource> Union(IAsyncEnumerable<TSource> next)