[Empty] add empty generator.

Author: reegeek

src/StructLinq.Tests/EmptyTests.cs

@@ -0,0 +1,17 @@
+using FluentAssertions;
+using Xunit;
+
+namespace StructLinq.Tests
+{
+    public class EmptyTests
+    {
+        [Fact]
+        public void ShouldBeEmpty()
+        {
+            StructEnumerable.Empty<int>()
+                            .ToArray()
+                            .Should()
+                            .BeEmpty();
+        }
+    }
+}

src/StructLinq/Empty/EmptyEnumerable.cs

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+using System.Runtime.CompilerServices;
+
+namespace StructLinq.Empty
+{
+    public struct EmptyEnumerable<T> : IStructEnumerable<T, EmptyEnumerator<T>>
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public readonly EmptyEnumerator<T> GetEnumerator()
+        {
+            return new EmptyEnumerator<T>();
+        }
+    }
+}

src/StructLinq/Empty/EmptyEnumerator.cs

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+using System;
+using System.Runtime.CompilerServices;
+
+namespace StructLinq.Empty
+{
+    public struct EmptyEnumerator<T> : IStructEnumerator<T>
+    {
+        public void Dispose()
+        {
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public bool MoveNext()
+        {
+            return false;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Reset()
+        {
+        }
+
+        public T Current
+        {
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            get => throw new NotImplementedException();
+        }
+    }
+}

src/StructLinq/Empty/StructEnumerable.Empty.cs

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+using System.Runtime.CompilerServices;
+using StructLinq.Empty;
+
+// ReSharper disable once CheckNamespace
+namespace StructLinq
+{
+    public static partial class StructEnumerable
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static EmptyEnumerable<T> Empty<T>()
+        {
+            return new EmptyEnumerable<T>();
+        }
+    }
+}