Added also JsonConverter for Unit

src/FuncSharp.Tests/Product/UnitJsonConverterTests.cs

@@ -0,0 +1,70 @@
+using System.Text.Json;
+using Xunit;
+
+namespace FuncSharp.Tests;
+
+public class UnitJsonConverterTests
+{
+    private record DummyObjectWithUnit(string PropertyBefore, Unit Unit, string PropertyAfter);
+
+    [Fact]
+    public void Serializes_unit_only()
+    {
+        // Act
+        var json = JsonSerializer.Serialize(Unit.Value);
+
+        // Assert
+        Assert.Equal("{}", json);
+    }
+
+    [Fact]
+    public void Deserializes_unit_only()
+    {
+        // Act
+        var value = JsonSerializer.Deserialize<Unit>("{}");
+
+        // Assert
+        Assert.Equal(Unit.Value, value);
+    }
+
+    [Fact]
+    public void Serializes_complex_object_including_unit()
+    {
+        // Arrange
+        var value = new DummyObjectWithUnit("before", Unit.Value, "after");
+
+        // Act
+        var json = JsonSerializer.Serialize(value);
+
+        // Assert
+        Assert.Equal(@"{""PropertyBefore"":""before"",""Unit"":{},""PropertyAfter"":""after""}", json);
+    }
+
+    [Fact]
+    public void Deserializes_complex_object_including_unit()
+    {
+        // Arrange
+        var json = @"{""PropertyBefore"":""before"",""Unit"":{},""PropertyAfter"":""after""}";
+
+        // Act
+        var value = JsonSerializer.Deserialize<DummyObjectWithUnit>(json);
+
+        // Assert
+        Assert.Equal("before", value.PropertyBefore);
+        Assert.Equal(Unit.Value, value.Unit);
+        Assert.Equal("after", value.PropertyAfter);
+    }
+
+    [Fact]
+    public void Serializes_try_with_success_as_unit()
+    {
+        // Arrange
+        var value = Try.Success<Unit, string>(Unit.Value);
+
+        // Act
+        var json = JsonSerializer.Serialize(value);
+
+        // Assert
+        Assert.Equal(@"{""IsSuccess"":true,""Value"":{}}", json);
+    }
+}

src/FuncSharp/Product/Unit.cs

@@ -1,9 +1,12 @@
 
+using System.Text.Json.Serialization;
+
 namespace FuncSharp;
 
 /// <summary>
 /// The Unit type (product of zero types). It has only one instance.
 /// </summary>
+[JsonConverter(typeof(UnitJsonConverter))]
 public sealed class Unit : Product0
 {
     private Unit()

src/FuncSharp/Product/UnitJsonConverter.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace FuncSharp;
+
+public sealed class UnitJsonConverter : JsonConverter<Unit>
+{
+    public override Unit Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        reader.Read();
+        return Unit.Value;
+    }
+
+    public override void Write(Utf8JsonWriter writer, Unit value, JsonSerializerOptions options)
+    {
+        writer.WriteStartObject();
+        writer.WriteEndObject();
+    }
+}