More efficient parsing of case classes with 1 to 22 fields

Author: plokhotnyuk

zio-schema-json/shared/src/main/scala/zio/schema/codec/JsonCodec.scala

@@ -1540,7 +1540,7 @@ object JsonCodec {
   //scalafmt: { maxColumn = 120, optIn.configStyleArguments = true }
 
   private class CaseClassJsonDecoder[Z](
-    fields: Array[Schema.Field[Z, _]],
+    defaults: Array[Any],
     fieldDecoders: Array[ZJsonDecoder[_]],
     spans: Array[JsonError.ObjectAccess],
     stringMatrix: StringMatrix,
@@ -1549,7 +1549,7 @@ object JsonCodec {
   ) {
 
     def unsafeDecodeFields(trace: List[JsonError], in: RetractReader): Array[Any] = {
-      val len    = fields.length
+      val len    = defaults.length
       val buffer = new Array[Any](len)
       var reader = in
       var continue =
@@ -1566,28 +1566,17 @@ object JsonCodec {
         else if (idx >= 0) {
           if (buffer(idx) != null) error(trace, "duplicate")
           else buffer(idx) = fieldDecoders(idx).unsafeDecode(spans(idx) :: trace, reader)
-        } else if (!rejectExtraFields) Lexer.skipValue(trace, reader)
-        else error(trace, "extra field")
+        } else if (rejectExtraFields) error(trace, "extra field")
+        else Lexer.skipValue(trace, reader)
         continue = Lexer.nextField(trace, reader)
         pos += 1
       }
       var idx = 0
       while (idx < len) {
         if (buffer(idx) == null) {
-          val field = fields(idx)
-          if ((field.optional || field.transient) && field.defaultValue.isDefined) {
-            buffer(idx) = field.defaultValue.get
-          } else {
-            val schema = field.schema match {
-              case l @ Schema.Lazy(_) => l.schema
-              case s                  => s
-            }
-            buffer(idx) = schema match {
-              case _: Schema.Optional[_]               => None
-              case collection: Schema.Collection[_, _] => collection.empty
-              case _                                   => error(spans(idx) :: trace, "missing")
-            }
-          }
+          val default = defaults(idx)
+          if (default == null) error(spans(idx) :: trace, "missing")
+          buffer(idx) = default
         }
         idx += 1
       }
@@ -1602,26 +1591,38 @@ object JsonCodec {
 
     def apply[Z](schema: Schema.Record[Z], discriminator: Int): CaseClassJsonDecoder[Z] = {
       val len      = schema.fields.length
-      val fields   = new Array[Schema.Field[Z, _]](len)
+      val defaults = new Array[Any](len)
       val decoders = new Array[ZJsonDecoder[_]](len)
       val spans    = new Array[JsonError.ObjectAccess](len)
       val names    = new Array[String](len)
       val aliases  = Array.newBuilder[(String, Int)]
-      var i        = 0
+      var idx      = 0
       schema.fields.foreach { field =>
         val name = field.name.asInstanceOf[String]
-        fields(i) = field
-        names(i) = name
-        spans(i) = JsonError.ObjectAccess(name)
-        decoders(i) = schemaDecoder(field.schema)
+        names(idx) = name
+        spans(idx) = JsonError.ObjectAccess(name)
+        decoders(idx) = schemaDecoder(field.schema)
         field.annotations.foreach {
-          case annotation: fieldNameAliases => annotation.aliases.foreach(a => aliases += ((a, i)))
+          case annotation: fieldNameAliases => annotation.aliases.foreach(a => aliases += ((a, idx)))
           case _                            =>
         }
-        i += 1
+        defaults(idx) =
+          if ((field.optional || field.transient) && field.defaultValue.isDefined) field.defaultValue.get
+          else {
+            val schema = field.schema match {
+              case l @ Schema.Lazy(_) => l.schema
+              case s                  => s
+            }
+            schema match {
+              case _: Schema.Optional[_]               => None
+              case collection: Schema.Collection[_, _] => collection.empty
+              case _                                   => null
+            }
+          }
+        idx += 1
       }
       new CaseClassJsonDecoder(
-        fields,
+        defaults,
         decoders,
         spans,
         new StringMatrix(names, aliases.result()),