Fix "Unfold" bug so iterations are repeatable

morelinq · Apr 1, 2023 · 034ba56 · 034ba56
1 parent 93bc6dc
commit 034ba56
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Showing 2 changed files with 15 additions and 2 deletions.
diff --git a/MoreLinq.Test/UnfoldTest.cs b/MoreLinq.Test/UnfoldTest.cs
@@ -81,5 +81,18 @@ public void UnfoldEmptySequence()
                                                   e => e.Result);
             Assert.That(result, Is.Empty);
         }
+
+        [Test(Description = "https://github.com/morelinq/MoreLINQ/issues/990")]
+        public void UnfoldReiterationsReturnsSameResult()
+        {
+            var xs = MoreEnumerable.Unfold(1, n => (Result: n, Next: n + 1),
+                                           _ => true,
+                                           n => n.Next,
+                                           n => n.Result)
+                                   .Take(5);
+
+            xs.AssertSequenceEqual(1, 2, 3, 4, 5);
+            xs.AssertSequenceEqual(1, 2, 3, 4, 5);
+        }
     }
 }
diff --git a/MoreLinq/Unfold.cs b/MoreLinq/Unfold.cs
@@ -61,9 +61,9 @@ public static IEnumerable<TResult> Unfold<TState, T, TResult>(
             if (stateSelector == null) throw new ArgumentNullException(nameof(stateSelector));
             if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));
 
-            return _(); IEnumerable<TResult> _()
+            return _(state); IEnumerable<TResult> _(TState initialState)
             {
-                while (true)
+                for (var state = initialState; ;)
                 {
                     var step = generator(state);