fix discriminator on abstract classes

fix [feature request] Allow fields and properties of Type ISomeInterface #11

src/Dahomey.Cbor.Tests/Issues/Issue0020.cs

@@ -0,0 +1,74 @@
+using Dahomey.Cbor.Attributes;
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Xunit;
+
+namespace Dahomey.Cbor.Tests.Issues
+{
+    public class Issue0020
+    {
+        public class Tree
+        {
+            [CborProperty("age")]
+            public readonly int _age;
+
+            [CborProperty("fruit")]
+            public Fruit _fruit;
+
+            [CborConstructor]
+            public Tree(int age, Fruit fruit)
+            {
+                _age = age;
+                _fruit = fruit;
+            }
+        }
+
+        public abstract class Fruit
+        {
+            public string id2 = "myid"; // if I remove this it won't throw
+        }
+
+        [CborDiscriminator("Apple")]
+        public class Apple : Fruit
+        {
+            [CborProperty("type")]
+            public const string type = "I am an apple";
+        }
+
+        [CborDiscriminator("Orange")]
+        public class Orange : Fruit
+        {
+            [CborProperty("type")]
+            public const string type = "I am an orange";
+        }
+
+        [Fact]
+        public void TestWrite()
+        {
+            CborOptions options = new CborOptions();
+            options.Registry.DefaultDiscriminatorConvention.RegisterAssembly(typeof(Fruit).Assembly);
+
+            Tree tree = new Tree(10, new Apple());
+
+            const string hexBuffer = "A2636167650A656672756974A3625F74654170706C6564747970656D4920616D20616E206170706C6563696432646D796964";
+            Helper.TestWrite(tree, hexBuffer, null, options);
+        }
+
+        [Fact]
+        public void TestRead()
+        {
+            CborOptions options = new CborOptions();
+            options.Registry.DefaultDiscriminatorConvention.RegisterAssembly(typeof(Fruit).Assembly);
+
+            const string hexBuffer = "A2636167650A656672756974A3625F74654170706C6564747970656D4920616D20616E206170706C6563696432646D796964";
+            Tree tree = Helper.Read<Tree>(hexBuffer, options);
+
+            Assert.NotNull(tree);
+            Assert.Equal(10, tree._age);
+            Assert.NotNull(tree._fruit);
+            Assert.IsType<Apple>(tree._fruit);
+            Assert.Equal("myid", ((Apple)tree._fruit).id2);
+        }
+    }
+}

src/Dahomey.Cbor/Serialization/Converters/ObjectConverter.cs

@@ -199,7 +199,7 @@ public override void Write(ref CborWriter writer, T value)
                 obj = value,
             };
 
-            if (!_isInterfaceOrAbstract && value.GetType() != typeof(T))
+            if (_objectMapping.CreatorMapping == null && value.GetType() != typeof(T))
             {
                 context.state = MapWriterContext.State.Discriminator;
                 context.objectConverter = (IObjectConverter)_registry.ConverterRegistry.Lookup(value.GetType());