Make Optional<T> into readonly struct to avoid heap allocations

src/DotTiled.Tests/Assert/AssertLayer.cs

@@ -35,8 +35,7 @@ public static partial class DotTiledAssert
     AssertEqual(expected.X, actual.X, nameof(TileLayer.X));
     AssertEqual(expected.Y, actual.Y, nameof(TileLayer.Y));
 
-    Assert.NotNull(actual.Data);
-    AssertData(expected.Data, actual.Data);
+    AssertOptionalsEqual(expected.Data, actual.Data, nameof(TileLayer.Data), AssertData);
   }
 
   private static void AssertLayer(ObjectLayer expected, ObjectLayer actual)
@@ -60,8 +59,7 @@ public static partial class DotTiledAssert
     AssertEqual(expected.X, actual.X, nameof(ImageLayer.X));
     AssertEqual(expected.Y, actual.Y, nameof(ImageLayer.Y));
 
-    Assert.NotNull(actual.Image);
-    AssertImage(expected.Image, actual.Image);
+    AssertOptionalsEqual(expected.Image, actual.Image, nameof(ImageLayer.Image), AssertImage);
   }
 
   private static void AssertLayer(Group expected, Group actual)

src/DotTiled.Tests/Assert/AssertMap.cs

@@ -33,12 +33,6 @@ public static partial class DotTiledAssert
     string nameof,
     Action<T, T> assertEqual)
   {
-    if (expected is null)
-    {
-      Assert.Null(actual);
-      return;
-    }
-
     if (expected.HasValue)
     {
       Assert.True(actual.HasValue, $"Expected {nameof} to have a value");
@@ -51,12 +45,6 @@ public static partial class DotTiledAssert
 
   internal static void AssertEqual<T>(Optional<T> expected, Optional<T> actual, string nameof)
   {
-    if (expected is null)
-    {
-      Assert.Null(actual);
-      return;
-    }
-
     if (expected.HasValue)
     {
       Assert.True(actual.HasValue, $"Expected {nameof} to have a value");

src/DotTiled.Tests/TestData/Maps/map-with-common-props/map-with-common-props.cs

@@ -58,7 +58,7 @@ public partial class TestData
       new IntProperty { Name = "intprop", Value = 8 },
       new ObjectProperty { Name = "objectprop", Value = 5 },
       new StringProperty { Name = "stringprop", Value = "This is a string, hello world!" },
-      new ColorProperty { Name = "unsetcolorprop", Value = Optional<Color>.Empty }
+      new ColorProperty { Name = "unsetcolorprop", Value = Optional.Empty }
     ]
   };
 }

src/DotTiled.Tests/UnitTests/OptionalTests.cs

@@ -59,30 +59,6 @@ public class OptionalTests
     Assert.Equal(expectedValue, optional.Value);
   }
 
-  [Fact]
-  public void ImplicitConversion_FromOptionalToValue_ShouldReturnValue_WhenHasValueIsTrue()
-  {
-    // Arrange
-    int expectedValue = 10;
-    var optional = new Optional<int>(expectedValue);
-
-    // Act
-    int value = optional;
-
-    // Assert
-    Assert.Equal(expectedValue, value);
-  }
-
-  [Fact]
-  public void ImplicitConversion_FromOptionalToValue_ShouldThrowException_WhenHasValueIsFalse()
-  {
-    // Arrange
-    var optional = new Optional<int>();
-
-    // Act & Assert
-    _ = Assert.Throws<InvalidOperationException>(() => { int value = optional; });
-  }
-
   // ToString Method Tests
 
   [Fact]
@@ -237,18 +213,6 @@ public class OptionalTests
     _ = Assert.Throws<InvalidOperationException>(() => optional.Value);
   }
 
-  [Fact]
-  public void ImplicitConversion_WhenHasValueIsFalse_ShouldThrowInvalidOperationException()
-  {
-    // Arrange
-    var optional = new Optional<int>();
-
-    // Act & Assert
-    _ = Assert.Throws<InvalidOperationException>(() => { int value = optional; });
-  }
-
-  // Edge Cases
-
   [Fact]
   public void EmptyOptionalEquality_ShouldReturnTrue()
   {

src/DotTiled.Tests/UnitTests/Serialization/LoaderTests.cs

@@ -71,8 +71,8 @@ public class LoaderTests
     """);
 
     var resourceCache = Substitute.For<IResourceCache>();
-    resourceCache.GetTileset(Arg.Any<string>()).Returns(Optional<Tileset>.Empty);
-    resourceCache.GetTemplate(Arg.Any<string>()).Returns(Optional<Template>.Empty);
+    resourceCache.GetTileset(Arg.Any<string>()).Returns(Optional.Empty);
+    resourceCache.GetTemplate(Arg.Any<string>()).Returns(Optional.Empty);
 
     var customTypeDefinitions = Enumerable.Empty<ICustomTypeDefinition>();
     var loader = new Loader(resourceReader, resourceCache, customTypeDefinitions);
@@ -134,8 +134,8 @@ public class LoaderTests
     """);
 
     var resourceCache = Substitute.For<IResourceCache>();
-    resourceCache.GetTileset(Arg.Any<string>()).Returns(Optional<Tileset>.Empty);
-    resourceCache.GetTemplate(Arg.Any<string>()).Returns(Optional<Template>.Empty);
+    resourceCache.GetTileset(Arg.Any<string>()).Returns(Optional.Empty);
+    resourceCache.GetTemplate(Arg.Any<string>()).Returns(Optional.Empty);
 
     var customTypeDefinitions = Enumerable.Empty<ICustomTypeDefinition>();
     var loader = new Loader(resourceReader, resourceCache, customTypeDefinitions);
@@ -219,7 +219,7 @@ public class LoaderTests
     """);
 
     var resourceCache = Substitute.For<IResourceCache>();
-    resourceCache.GetTileset(Arg.Any<string>()).Returns(Optional<Tileset>.Empty);
+    resourceCache.GetTileset(Arg.Any<string>()).Returns(Optional.Empty);
     resourceCache.GetTemplate("template.tx").Returns(new Optional<Template>(new Template
     {
       Object = new PolygonObject

src/DotTiled.Tests/UnitTests/Serialization/MapReaderTests.cs

@@ -39,7 +39,7 @@ public partial class MapReaderTests
           return new Optional<ICustomTypeDefinition>(ctd);
         }
 
-        return Optional<ICustomTypeDefinition>.Empty;
+        return Optional.Empty;
       }
       using var mapReader = new MapReader(mapString, ResolveTileset, ResolveTemplate, ResolveCustomType);
 

src/DotTiled.Tests/UnitTests/Serialization/Tmj/TmjMapReaderTests.cs

@@ -35,7 +35,7 @@ public partial class TmjMapReaderTests
         return new Optional<ICustomTypeDefinition>(ctd);
       }
 
-      return Optional<ICustomTypeDefinition>.Empty;
+      return Optional.Empty;
     }
     using var mapReader = new TmjMapReader(json, ResolveTileset, ResolveTemplate, ResolveCustomType);
 

src/DotTiled.Tests/UnitTests/Serialization/Tmx/TmxMapReaderTests.cs

@@ -35,7 +35,7 @@ public partial class TmxMapReaderTests
         return new Optional<ICustomTypeDefinition>(ctd);
       }
 
-      return Optional<ICustomTypeDefinition>.Empty;
+      return Optional.Empty;
     }
     using var mapReader = new TmxMapReader(reader, ResolveTileset, ResolveTemplate, ResolveCustomType);