optimize the first and last operator for a frozen-sequence and optimize the frozen-sequence value-enumerator

Benchmarks/Benchmarks/FirstOperatorBenchmark.cs

@@ -21,12 +21,18 @@ public void Setup()
     [Benchmark(Baseline = true)]
     public void FrozenSequenceFirst()
     {
-        _ = _frozenSequence!.First(number => number is 50);
+        for (var i = 0; i < 3; i++)
+        {
+            _ = _frozenSequence!.First(number => number is 50);
+        }
     }
 
     [Benchmark]
     public void ListFirst()
     {
-        _ = _list!.First(number => number is 50);
+        for (var i = 0; i < 3; i++)
+        {
+            _ = _list!.First(number => number is 50);
+        }
     }
 }

Benchmarks/Benchmarks/LastOperatorBenchmark.cs

@@ -0,0 +1,38 @@
+using BenchmarkDotNet.Attributes;
+using Falko.Common.Extensions;
+using Falko.Common.Sequences;
+
+namespace Benchmarks;
+
+public class LastOperatorBenchmark
+{
+    private List<int>? _list;
+
+    private FrozenSequence<int>? _frozenSequence;
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        _frozenSequence = Enumerable.Range(0, 100).ToFrozenSequence();
+
+        _list = Enumerable.Range(0, 100).ToList();
+    }
+
+    [Benchmark(Baseline = true)]
+    public void FrozenSequenceFirst()
+    {
+        for (var i = 0; i < 3; i++)
+        {
+            _ = _frozenSequence!.Last(number => number is 50);
+        }
+    }
+
+    [Benchmark]
+    public void ListFirst()
+    {
+        for (var i = 0; i < 3; i++)
+        {
+            _ = _list!.Last(number => number is 50);
+        }
+    }
+}

Benchmarks/Benchmarks/Program.cs

@@ -1,8 +1,5 @@
 using BenchmarkDotNet.Running;
 using Benchmarks;
 
-var b = new FirstOperatorBenchmark();
-b.Setup();
-b.FrozenSequenceFirst();
-b.ListFirst();
 BenchmarkRunner.Run<FirstOperatorBenchmark>();
+BenchmarkRunner.Run<LastOperatorBenchmark>();

Falko.Common.slnx

@@ -23,4 +23,4 @@
     <Project Path="Sources\Falko.Common.Sequences\Falko.Common.Sequences.csproj" Type="Classic C#" />
   </Folder>
   <Folder Name="/Tests/" />
-</Solution>
+</Solution>

Sources/Falko.Common.Sequences/Asserts/SequenceExceptions.cs

@@ -67,7 +67,6 @@ public static void ThrowIfNotSingle(int count)
     }
 
     [DoesNotReturn]
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static void ThrowNotMatchAny()
     {
         throw new InvalidOperationException("The source sequence does not match any of the specified conditions.");

Sources/Falko.Common.Sequences/Sequences/FrozenSequence.Operator.First.cs

@@ -20,13 +20,19 @@ public T First(Func<T, bool> predicate)
     {
         ArgumentNullException.ThrowIfNull(predicate);
 
-        foreach (ref readonly var item in this)
+        var itemsCount = _itemsCount;
+
+        scoped ref var itemsReference = ref MemoryMarshal.GetArrayDataReference(_items);
+
+        for (var itemIndex = 0; itemIndex < itemsCount; itemIndex++)
         {
+            var item = Unsafe.Add(ref itemsReference, itemIndex);
+
             if (predicate(item)) return item;
         }
 
         SequenceExceptions.ThrowNotMatchAny();
-        return default!; // This line is unreachable
+        return default; // This line is unreachable
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -41,8 +47,14 @@ public T First(Func<T, bool> predicate)
     {
         ArgumentNullException.ThrowIfNull(predicate);
 
-        foreach (ref readonly var item in this)
+        var itemsCount = _itemsCount;
+
+        scoped ref var itemsReference = ref MemoryMarshal.GetArrayDataReference(_items);
+
+        for (var itemIndex = 0; itemIndex < itemsCount; itemIndex++)
         {
+            var item = Unsafe.Add(ref itemsReference, itemIndex);
+
             if (predicate(item)) return item;
         }
 

Sources/Falko.Common.Sequences/Sequences/FrozenSequence.Operator.Last.cs

@@ -19,12 +19,10 @@ public T Last()
 
     public T Last(Func<T, bool> predicate)
     {
-        var itemsCount = _itemsCount;
-
-        SequenceExceptions.ThrowIfEmpty(itemsCount);
-
         ArgumentNullException.ThrowIfNull(predicate);
 
+        var itemsCount = _itemsCount;
+
         scoped ref var itemsReference = ref MemoryMarshal.GetArrayDataReference(_items);
 
         for (var itemIndex = itemsCount - 1; itemIndex >= 0; itemIndex--)
@@ -50,12 +48,10 @@ public T Last(Func<T, bool> predicate)
 
     public T? LastOrDefault(Func<T, bool> predicate)
     {
-        var itemsCount = _itemsCount;
-
-        if (itemsCount is 0) return default;
-
         ArgumentNullException.ThrowIfNull(predicate);
 
+        var itemsCount = _itemsCount;
+
         scoped ref var itemsReference = ref MemoryMarshal.GetArrayDataReference(_items);
 
         for (var itemIndex = itemsCount - 1; itemIndex >= 0; itemIndex--)

Sources/Falko.Common.Sequences/Sequences/FrozenSequence.ValueEnumerator.cs

@@ -16,6 +16,7 @@ public ref struct ValueEnumerator
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal ValueEnumerator(T[] values, int valuesCount)
         {
+            _currentIndex = -1;
             _valuesReference = ref MemoryMarshal.GetArrayDataReference(values);
             _valuesCount = valuesCount;
         }
@@ -29,19 +30,18 @@ public ref readonly T Current
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public bool MoveNext()
         {
-            var currentIndex = _currentIndex;
+            var nextIndex = _currentIndex + 1;
 
-            if (currentIndex == _valuesCount) return false;
-
-            _currentIndex = currentIndex + 1;
+            if (nextIndex >= _valuesCount) return false;
 
+            _currentIndex = nextIndex;
             return true;
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void Reset()
         {
-            _currentIndex = 0;
+            _currentIndex = -1;
         }
     }
 }