From 753c7d4bb148c826c0f5e5bef838837854139f26 Mon Sep 17 00:00:00 2001
From: Atif Aziz <code@raboof.com>
Date: Wed, 17 Mar 2021 23:55:54 +0100
Subject: [PATCH] Fix "TrySingle" signature with honest NRT annotations

---
 MoreLinq/Experimental/TrySingle.cs | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/MoreLinq/Experimental/TrySingle.cs b/MoreLinq/Experimental/TrySingle.cs
index 6be3f8212..e72bfbc82 100644
--- a/MoreLinq/Experimental/TrySingle.cs
+++ b/MoreLinq/Experimental/TrySingle.cs
@@ -51,7 +51,7 @@ partial class ExperimentalEnumerable
         /// than two elements from the sequence.
         /// </remarks>
 
-        public static (TCardinality Cardinality, T Value)
+        public static (TCardinality Cardinality, T? Value)
             TrySingle<T, TCardinality>(this IEnumerable<T> source,
                 TCardinality zero, TCardinality one, TCardinality many) =>
             TrySingle(source, zero, one, many, ValueTuple.Create);
@@ -96,11 +96,7 @@ public static (TCardinality Cardinality, T Value)
 
         public static TResult TrySingle<T, TCardinality, TResult>(this IEnumerable<T> source,
             TCardinality zero, TCardinality one, TCardinality many,
-            // TODO review second argument of resultSelector
-            // ...that can be defaulted to null for nullable references
-            // so the signature is not quite accurate, but can we do
-            // something about that?
-            Func<TCardinality, T, TResult> resultSelector)
+            Func<TCardinality, T?, TResult> resultSelector)
         {
             if (source == null) throw new ArgumentNullException(nameof(source));
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
@@ -108,7 +104,7 @@ public static TResult TrySingle<T, TCardinality, TResult>(this IEnumerable<T> so
             switch (source.TryGetCollectionCount())
             {
                 case 0:
-                    return resultSelector(zero, default!);
+                    return resultSelector(zero, default);
                 case 1:
                 {
                     var item = source switch
@@ -120,15 +116,15 @@ public static TResult TrySingle<T, TCardinality, TResult>(this IEnumerable<T> so
                     return resultSelector(one, item);
                 }
                 case {}:
-                    return resultSelector(many, default!);
+                    return resultSelector(many, default);
                 default:
                 {
                     using var e = source.GetEnumerator();
                     if (!e.MoveNext())
-                        return resultSelector(zero, default!);
+                        return resultSelector(zero, default);
                     var current = e.Current;
                     return !e.MoveNext() ? resultSelector(one, current)
-                                         : resultSelector(many, default!);
+                                         : resultSelector(many, default);
                 }
             }
         }