Implement struct record serialization with Reflection.Emit

Author: Tarmil

benchmarks/FSharp.SystemTextJson.Benchmarks/Program.fs

@@ -22,6 +22,12 @@ type TestRecord =
       thing: bool option
       time: System.DateTimeOffset }
 
+[<Struct>]
+type TestStructRecord = 
+    { name: string
+      thing: bool voption
+      time: System.DateTimeOffset }
+
 type SimpleClass() =
     member val Name: string = null with get, set
     member val Thing: bool option = None with get, set
@@ -58,7 +64,7 @@ type ArrayTestBase<'t>(instance: 't) =
     [<Benchmark>]
     member this.Deserialize_SystemTextJson () = System.Text.Json.JsonSerializer.Deserialize<'t[]>(this.Serialized, systemTextOptions)
 
-let recordInstance = 
+let recordInstance : TestRecord = 
     { name = "sample"
       thing = Some true
       time = System.DateTimeOffset.UnixEpoch.AddDays(200.) }
@@ -67,6 +73,14 @@ let recordInstance =
 type Records () =
     inherit ArrayTestBase<TestRecord>(recordInstance)
 
+let recordStructInstance : TestStructRecord = 
+    { name = "sample"
+      thing = ValueSome true
+      time = System.DateTimeOffset.UnixEpoch.AddDays(200.) }
+
+type StructRecords () =
+    inherit ArrayTestBase<TestStructRecord>(recordStructInstance)
+
 type Classes() =
     inherit ArrayTestBase<SimpleClass>(SimpleClass(Name = "sample", Thing = Some true, Time = DateTimeOffset.UnixEpoch.AddDays(200.)))
 
@@ -106,7 +120,7 @@ let config =
             .With(ExecutionValidator.FailOnError)
 
 let defaultSwitch () =
-    BenchmarkSwitcher([| typeof<Records>; typeof<Classes>; typeof<ReflectionComparison> |])
+    BenchmarkSwitcher([| typeof<Records>; typeof<StructRecords>; typeof<Classes>; typeof<ReflectionComparison> |])
 
 
 [<EntryPoint>]

src/FSharp.SystemTextJson/Record.fs

@@ -8,7 +8,7 @@ open FSharp.Reflection
 type JsonRecordConverter<'T>() =
     inherit JsonConverter<'T>()
 
-    static let fieldProps = RecordField<'T>.properties()
+    static let fieldProps = RecordField<'T>.fields()
 
     static let expectedFieldCount =
         fieldProps
@@ -54,11 +54,10 @@ type JsonRecordConverter<'T>() =
 
     override __.Write(writer, value, options) =
         writer.WriteStartObject()
-        fieldProps
-        |> Array.iter (fun p ->
+        for p in fieldProps do
             if not p.Ignore then
                 writer.WritePropertyName(p.Name)
-                p.Serialize.Invoke(writer, value, options))
+                p.Serialize.Invoke(writer, value, options)
         writer.WriteEndObject()
 
 type JsonRecordConverter() =

src/FSharp.SystemTextJson/RecordField.fs

@@ -6,15 +6,14 @@ open FSharp.Reflection
 open System.Reflection.Emit
 open System.Text.Json
 
-type internal Serializer<'Record> = delegate of Utf8JsonWriter * 'Record * JsonSerializerOptions -> unit
-type internal FieldReader<'Record, 'Field> = delegate of 'Record -> 'Field
+type internal Serializer = Action<Utf8JsonWriter, obj, JsonSerializerOptions>
 
 type internal RecordField<'Record> =
     {
         Name: string
         Type: Type
         Ignore: bool
-        Serialize: Serializer<'Record>
+        Serialize: Serializer
     }
 
     static member name (p: PropertyInfo) =
@@ -39,15 +38,17 @@ type internal RecordField<'Record> =
                 )
             let gen = dynMethod.GetILGenerator()
             gen.Emit(OpCodes.Ldarg_0)
+            if f.DeclaringType.IsValueType then
+                gen.Emit(OpCodes.Unbox, typeof<'Record>)
             gen.Emit(OpCodes.Ldfld, f)
             gen.Emit(OpCodes.Ret)
-            dynMethod.CreateDelegate(typeof<FieldReader<'Record, 'Field>>) :?> FieldReader<'Record, 'Field>
-        Serializer<'Record>(fun writer r options ->
+            dynMethod.CreateDelegate(typeof<Func<obj, 'Field>>) :?> Func<obj, 'Field>
+        Serializer(fun writer r options ->
             let v = getter.Invoke(r)
             JsonSerializer.Serialize<'Field>(writer, v, options)
         )
 
-    static member properties () =
+    static member fields () =
         let recordTy = typeof<'Record>
         let fields = recordTy.GetFields(BindingFlags.Instance ||| BindingFlags.NonPublic)
         let props = FSharpType.GetRecordFields(recordTy, true)
@@ -57,7 +58,7 @@ type internal RecordField<'Record> =
                 typeof<RecordField<'Record>>.GetMethod("serializer", BindingFlags.Static ||| BindingFlags.NonPublic)
                     .MakeGenericMethod(p.PropertyType)
                     .Invoke(null, [|f|])
-                    :?> Serializer<'Record>
+                    :?> Serializer
             {
                 Name = RecordField<'Record>.name p
                 Type = p.PropertyType