[Kotlin] Support for optional scalars. (#6115)

More information on #6014

7 files changed, 464 insertions, 32 deletions

diff --git a/include/flatbuffers/idl.h b/include/flatbuffers/idl.h
index 6b0de14a..a361c653 100644
--- a/include/flatbuffers/idl.h
+++ b/include/flatbuffers/idl.h
@@ -305,6 +305,10 @@ struct FieldDef : public Definition {
 
   bool Deserialize(Parser &parser, const reflection::Field *field);
 
+  bool IsScalarOptional() const {
+    return IsScalar(value.type.base_type) && optional;
+  }
+
   Value value;
   bool deprecated;  // Field is allowed to be present in old data, but can't be.
                     // written in new data nor accessed in new code.
diff --git a/src/idl_gen_kotlin.cpp b/src/idl_gen_kotlin.cpp
index 2c0c8d43..79913f54 100644
--- a/src/idl_gen_kotlin.cpp
+++ b/src/idl_gen_kotlin.cpp
@@ -159,6 +159,24 @@ class KotlinGenerator : public BaseGenerator {
     }
   }
 
+  // with the addition of optional scalar types,
+  // we are adding the nullable '?' operator to return type of a field.
+  std::string GetterReturnType(const FieldDef &field) const {
+    auto base_type = field.value.type.base_type;
+
+    auto r_type = GenTypeGet(field.value.type);
+    if (field.IsScalarOptional() ||
+        // string, structs and unions
+        (base_type == BASE_TYPE_STRING || base_type == BASE_TYPE_STRUCT ||
+         base_type == BASE_TYPE_UNION) ||
+        // vector of anything not scalar
+        (base_type == BASE_TYPE_VECTOR &&
+         !IsScalar(field.value.type.VectorType().base_type))) {
+      r_type += "?";
+    }
+    return r_type;
+  }
+
   std::string GenTypeGet(const Type &type) const {
     return IsScalar(type.base_type) ? GenTypeBasic(type.base_type)
                                     : GenTypePointer(type);
@@ -179,6 +197,18 @@ class KotlinGenerator : public BaseGenerator {
   // - Floats are upcasted to doubles
   // - Unsigned are casted to signed
   std::string GenFBBDefaultValue(const FieldDef &field) const {
+    if (field.IsScalarOptional()) {
+      // although default value is null, java API forces us to present a real
+      // default value for scalars, while adding a field to the buffer. This is
+      // not a problem because the default can be representing just by not
+      // calling builder.addMyField()
+      switch (field.value.type.base_type) {
+        case BASE_TYPE_DOUBLE:
+        case BASE_TYPE_FLOAT: return "0.0";
+        case BASE_TYPE_BOOL: return "false";
+        default: return "0";
+      }
+    }
     auto out = GenDefaultValue(field, true);
     // All FlatBufferBuilder default floating point values are doubles
     if (field.value.type.base_type == BASE_TYPE_FLOAT) {
@@ -204,6 +234,8 @@ class KotlinGenerator : public BaseGenerator {
                               bool force_signed = false) const {
     auto &value = field.value;
     auto base_type = field.value.type.base_type;
+
+    if (field.IsScalarOptional()) { return "null"; }
     if (IsFloat(base_type)) {
       auto val = KotlinFloatGen.GenFloatConstant(field);
       if (base_type == BASE_TYPE_DOUBLE && val.back() == 'f') {
@@ -655,19 +687,22 @@ class KotlinGenerator : public BaseGenerator {
                         CodeWriter &writer, const IDLOptions options) const {
     auto field_type = GenTypeBasic(field.value.type.base_type);
     auto secondArg = MakeCamel(Esc(field.name), false) + ": " + field_type;
-    GenerateFunOneLine(writer, "add" + MakeCamel(Esc(field.name), true),
-                       "builder: FlatBufferBuilder, " + secondArg, "", [&]() {
-                         auto method = GenMethod(field.value.type);
-                         writer.SetValue("field_name",
-                                         MakeCamel(Esc(field.name), false));
-                         writer.SetValue("method_name", method);
-                         writer.SetValue("pos", field_pos);
-                         writer.SetValue("default", GenFBBDefaultValue(field));
-                         writer.SetValue("cast", GenFBBValueCast(field));
-
-                         writer += "builder.add{{method_name}}({{pos}}, \\";
-                         writer += "{{field_name}}{{cast}}, {{default}})";
-                       }, options.gen_jvmstatic);
+
+    GenerateFunOneLine(
+        writer, "add" + MakeCamel(Esc(field.name), true),
+        "builder: FlatBufferBuilder, " + secondArg, "",
+        [&]() {
+          auto method = GenMethod(field.value.type);
+          writer.SetValue("field_name", MakeCamel(Esc(field.name), false));
+          writer.SetValue("method_name", method);
+          writer.SetValue("pos", field_pos);
+          writer.SetValue("default", GenFBBDefaultValue(field));
+          writer.SetValue("cast", GenFBBValueCast(field));
+
+          writer += "builder.add{{method_name}}({{pos}}, \\";
+          writer += "{{field_name}}{{cast}}, {{default}})";
+        },
+        options.gen_jvmstatic);
   }
 
   static std::string ToSignedType(const Type &type) {
@@ -754,7 +789,8 @@ class KotlinGenerator : public BaseGenerator {
         } else {
           params << ": ";
         }
-        params << GenTypeBasic(field.value.type.base_type);
+        auto optional = field.IsScalarOptional() ? "?" : "";
+        params << GenTypeBasic(field.value.type.base_type) << optional;
       }
 
       GenerateFun(writer, name, params.str(), "Int", [&]() {
@@ -773,11 +809,16 @@ class KotlinGenerator : public BaseGenerator {
                               MakeCamel(Esc(field.name), true));
               writer.SetValue("field_name", MakeCamel(Esc(field.name), false));
 
+              // we wrap on null check for scalar optionals
+              writer +=
+                  field.IsScalarOptional() ? "{{field_name}}?.run { \\" : "\\";
+
               writer += "add{{camel_field_name}}(builder, {{field_name}}\\";
               if (!IsScalar(field.value.type.base_type)) {
                 writer += "Offset\\";
               }
-              writer += ")";
+              // we wrap on null check for scalar optionals
+              writer += field.IsScalarOptional() ? ") }" : ")";
             }
           }
         }
@@ -812,7 +853,7 @@ class KotlinGenerator : public BaseGenerator {
       auto field_name = MakeCamel(Esc(field.name), false);
       auto field_type = GenTypeGet(field.value.type);
       auto field_default_value = GenDefaultValue(field);
-      auto return_type = GenTypeGet(field.value.type);
+      auto return_type = GetterReturnType(field);
       auto bbgetter = ByteBufferGetter(field.value.type, "bb");
       auto ucast = CastToUsigned(field);
       auto offset_val = NumToString(field.value.offset);
@@ -829,14 +870,13 @@ class KotlinGenerator : public BaseGenerator {
       writer.SetValue("bbgetter", bbgetter);
       writer.SetValue("ucast", ucast);
 
-      auto opt_ret_type = return_type + "?";
       // Generate the accessors that don't do object reuse.
       if (value_base_type == BASE_TYPE_STRUCT) {
         // Calls the accessor that takes an accessor object with a
         // new object.
         // val pos
         //     get() = pos(Vec3())
-        GenerateGetterOneLine(writer, field_name, opt_ret_type, [&]() {
+        GenerateGetterOneLine(writer, field_name, return_type, [&]() {
           writer += "{{field_name}}({{field_type}}())";
         });
       } else if (value_base_type == BASE_TYPE_VECTOR &&
@@ -844,8 +884,8 @@ class KotlinGenerator : public BaseGenerator {
         // Accessors for vectors of structs also take accessor objects,
         // this generates a variant without that argument.
         // ex: fun weapons(j: Int) = weapons(Weapon(), j)
-        GenerateFunOneLine(writer, field_name, "j: Int", opt_ret_type, [&]() {
-          writer += "{{field_name}}({{return_type}}(), j)";
+        GenerateFunOneLine(writer, field_name, "j: Int", return_type, [&]() {
+          writer += "{{field_name}}({{field_type}}(), j)";
         });
       }
 
@@ -872,7 +912,7 @@ class KotlinGenerator : public BaseGenerator {
               // fun pos(obj: Vec3) : Vec3? = obj.__assign(bb_pos + 4, bb)
               // ? adds nullability annotation
               GenerateFunOneLine(
-                  writer, field_name, "obj: " + field_type, return_type + "?",
+                  writer, field_name, "obj: " + field_type, return_type,
                   [&]() { writer += "obj.__assign(bb_pos + {{offset}}, bb)"; });
             } else {
               // create getter with object reuse
@@ -887,8 +927,7 @@ class KotlinGenerator : public BaseGenerator {
               //  }
               // ? adds nullability annotation
               GenerateFun(
-                  writer, field_name, "obj: " + field_type, return_type + "?",
-                  [&]() {
+                  writer, field_name, "obj: " + field_type, return_type, [&]() {
                     auto fixed = field.value.type.struct_def->fixed;
 
                     writer.SetValue("seek", Indirect("o + bb_pos", fixed));
@@ -908,7 +947,7 @@ class KotlinGenerator : public BaseGenerator {
             //         return if (o != 0) __string(o + bb_pos) else null
             //     }
             // ? adds nullability annotation
-            GenerateGetter(writer, field_name, return_type + "?", [&]() {
+            GenerateGetter(writer, field_name, return_type, [&]() {
               writer += "val o = __offset({{offset}})";
               writer += "return if (o != 0) __string(o + bb_pos) else null";
             });
@@ -926,15 +965,13 @@ class KotlinGenerator : public BaseGenerator {
 
             auto vectortype = field.value.type.VectorType();
             std::string params = "j: Int";
-            std::string nullable = IsScalar(vectortype.base_type) ? "" : "?";
 
             if (vectortype.base_type == BASE_TYPE_STRUCT ||
                 vectortype.base_type == BASE_TYPE_UNION) {
               params = "obj: " + field_type + ", j: Int";
             }
 
-            auto ret_type = return_type + nullable;
-            GenerateFun(writer, field_name, params, ret_type, [&]() {
+            GenerateFun(writer, field_name, params, return_type, [&]() {
               auto inline_size = NumToString(InlineSize(vectortype));
               auto index = "__vector(o) + j * " + inline_size;
               auto not_found = NotFoundReturn(field.value.type.element);
@@ -959,8 +996,8 @@ class KotlinGenerator : public BaseGenerator {
             break;
           }
           case BASE_TYPE_UNION:
-            GenerateFun(writer, field_name, "obj: " + field_type,
-                        return_type + "?", [&]() {
+            GenerateFun(writer, field_name, "obj: " + field_type, return_type,
+                        [&]() {
                           writer += OffsetWrapperOneLine(
                               offset_val, bbgetter + "(obj, o + bb_pos)",
                               "null");
diff --git a/src/idl_parser.cpp b/src/idl_parser.cpp
index 90e07674..05b1b194 100644
--- a/src/idl_parser.cpp
+++ b/src/idl_parser.cpp
@@ -2263,7 +2263,8 @@ CheckedError Parser::CheckClash(std::vector<FieldDef *> &fields,
 
 bool Parser::SupportsOptionalScalars() const {
   return !(opts.lang_to_generate &
-    ~(IDLOptions::kRust | IDLOptions::kSwift | IDLOptions::kLobster));
+           ~(IDLOptions::kRust | IDLOptions::kSwift | IDLOptions::kLobster |
+             IDLOptions::kKotlin));
 }
 
 bool Parser::SupportsAdvancedUnionFeatures() const {
diff --git a/tests/KotlinTest.kt b/tests/KotlinTest.kt
index 538ab466..cdbd299a 100644
--- a/tests/KotlinTest.kt
+++ b/tests/KotlinTest.kt
@@ -15,6 +15,7 @@
  */
 
 import MyGame.Example.*
+import optional_scalars.*
 import com.google.flatbuffers.ByteBufferUtil
 import com.google.flatbuffers.FlatBufferBuilder
 import NamespaceA.*
@@ -77,7 +78,7 @@ class KotlinTest {
         TestVectorOfUnions()
 
         TestSharedStringPool()
-
+        TestScalarOptional()
         println("FlatBuffers test: completed successfully")
     }
 
@@ -467,5 +468,125 @@ class KotlinTest {
             assert(offset == fb.createSharedString(testString));
         }
     }
+
+    fun TestScalarOptional() {
+        val fbb = FlatBufferBuilder(1)
+        ScalarStuff.startScalarStuff(fbb)
+        var pos = ScalarStuff.endScalarStuff(fbb)
+        fbb.finish(pos)
+
+        var scalarStuff = ScalarStuff.getRootAsScalarStuff(fbb.dataBuffer())
+
+        assert(scalarStuff.justI8  == 0.toByte())
+        assert(scalarStuff.maybeI8 == null)
+        assert(scalarStuff.defaultI8 == 42.toByte())
+        assert(scalarStuff.justU8 == 0.toUByte())
+        assert(scalarStuff.maybeU8 == null)
+        assert(scalarStuff.defaultU8 == 42.toUByte())
+        assert(scalarStuff.justI16 == 0.toShort())
+        assert(scalarStuff.maybeI16 == null)
+        assert(scalarStuff.defaultI16 == 42.toShort())
+        assert(scalarStuff.justU16 == 0.toUShort())
+        assert(scalarStuff.maybeU16 == null)
+        assert(scalarStuff.defaultU16 == 42.toUShort())
+        assert(scalarStuff.justI32 == 0)
+        assert(scalarStuff.maybeI32 == null)
+        assert(scalarStuff.defaultI32 == 42)
+        assert(scalarStuff.justU32 == 0.toUInt())
+        assert(scalarStuff.maybeU32 == null)
+        assert(scalarStuff.defaultU32 == 42U)
+        assert(scalarStuff.justI64 == 0L)
+        assert(scalarStuff.maybeI64 == null)
+        assert(scalarStuff.defaultI64 == 42L)
+        assert(scalarStuff.justU64 == 0UL)
+        assert(scalarStuff.maybeU64 == null)
+        assert(scalarStuff.defaultU64 == 42UL)
+        assert(scalarStuff.justF32 == 0.0f)
+        assert(scalarStuff.maybeF32 == null)
+        assert(scalarStuff.defaultF32 == 42.0f)
+        assert(scalarStuff.justF64 == 0.0)
+        assert(scalarStuff.maybeF64 == null)
+        assert(scalarStuff.defaultF64 == 42.0)
+        assert(scalarStuff.justBool == false)
+        assert(scalarStuff.maybeBool == null)
+        assert(scalarStuff.defaultBool == true)
+
+        fbb.clear()
+ 
+        ScalarStuff.startScalarStuff(fbb)
+        ScalarStuff.addJustI8(fbb, 5.toByte())
+        ScalarStuff.addMaybeI8(fbb, 5.toByte())
+        ScalarStuff.addDefaultI8(fbb, 5.toByte())
+        ScalarStuff.addJustU8(fbb, 6.toUByte())
+        ScalarStuff.addMaybeU8(fbb, 6.toUByte())
+        ScalarStuff.addDefaultU8(fbb, 6.toUByte())
+        ScalarStuff.addJustI16(fbb, 7.toShort())
+        ScalarStuff.addMaybeI16(fbb, 7.toShort())
+        ScalarStuff.addDefaultI16(fbb, 7.toShort())
+        ScalarStuff.addJustU16(fbb, 8.toUShort())
+        ScalarStuff.addMaybeU16(fbb, 8.toUShort())
+        ScalarStuff.addDefaultU16(fbb, 8.toUShort())
+        ScalarStuff.addJustI32(fbb, 9)
+        ScalarStuff.addMaybeI32(fbb, 9)
+        ScalarStuff.addDefaultI32(fbb, 9)
+        ScalarStuff.addJustU32(fbb, 10.toUInt())
+        ScalarStuff.addMaybeU32(fbb, 10.toUInt())
+        ScalarStuff.addDefaultU32(fbb, 10.toUInt())
+        ScalarStuff.addJustI64(fbb, 11L)
+        ScalarStuff.addMaybeI64(fbb, 11L)
+        ScalarStuff.addDefaultI64(fbb, 11L)
+        ScalarStuff.addJustU64(fbb, 12UL)
+        ScalarStuff.addMaybeU64(fbb, 12UL)
+        ScalarStuff.addDefaultU64(fbb, 12UL)
+        ScalarStuff.addJustF32(fbb, 13.0f)
+        ScalarStuff.addMaybeF32(fbb, 13.0f)
+        ScalarStuff.addDefaultF32(fbb, 13.0f)
+        ScalarStuff.addJustF64(fbb, 14.0)
+        ScalarStuff.addMaybeF64(fbb, 14.0)
+        ScalarStuff.addDefaultF64(fbb, 14.0)
+        ScalarStuff.addJustBool(fbb, true)
+        ScalarStuff.addMaybeBool(fbb, true)
+        ScalarStuff.addDefaultBool(fbb, true)
+
+        pos = ScalarStuff.endScalarStuff(fbb)
+
+        fbb.finish(pos)
+
+        scalarStuff = ScalarStuff.getRootAsScalarStuff(fbb.dataBuffer())
+
+        assert(scalarStuff.justI8  == 5.toByte())
+        assert(scalarStuff.maybeI8 == 5.toByte())
+        assert(scalarStuff.defaultI8 == 5.toByte())
+        assert(scalarStuff.justU8 == 6.toUByte())
+        assert(scalarStuff.maybeU8 == 6.toUByte())
+        assert(scalarStuff.defaultU8 == 6.toUByte())
+        assert(scalarStuff.justI16 == 7.toShort())
+        assert(scalarStuff.maybeI16 == 7.toShort())
+        assert(scalarStuff.defaultI16 == 7.toShort())
+        assert(scalarStuff.justU16 == 8.toUShort())
+        assert(scalarStuff.maybeU16 == 8.toUShort())
+        assert(scalarStuff.defaultU16 == 8.toUShort())
+        assert(scalarStuff.justI32 == 9)
+        assert(scalarStuff.maybeI32 == 9)
+        assert(scalarStuff.defaultI32 == 9)
+        assert(scalarStuff.justU32 == 10u)
+        assert(scalarStuff.maybeU32 == 10u)
+        assert(scalarStuff.defaultU32 == 10u)
+        assert(scalarStuff.justI64 == 11L)
+        assert(scalarStuff.maybeI64 == 11L)
+        assert(scalarStuff.defaultI64 == 11L)
+        assert(scalarStuff.justU64 == 12UL)
+        assert(scalarStuff.maybeU64 == 12UL)
+        assert(scalarStuff.defaultU64 == 12UL)
+        assert(scalarStuff.justF32 == 13.0f)
+        assert(scalarStuff.maybeF32 == 13.0f)
+        assert(scalarStuff.defaultF32 == 13.0f)
+        assert(scalarStuff.justF64 == 14.0)
+        assert(scalarStuff.maybeF64 == 14.0)
+        assert(scalarStuff.defaultF64 == 14.0)
+        assert(scalarStuff.justBool == true)
+        assert(scalarStuff.maybeBool == true)
+        assert(scalarStuff.defaultBool == true)
+    }
   }
 }
diff --git a/tests/generate_code.sh b/tests/generate_code.sh
index 56786fa2..c0a08330 100755
--- a/tests/generate_code.sh
+++ b/tests/generate_code.sh
@@ -53,7 +53,7 @@ $TEST_NOINCL_FLAGS $TEST_CPP_FLAGS $TEST_CS_FLAGS $TEST_JS_TS_FLAGS -o namespace
 ../flatc --dart monster_extra.fbs
 
 # Generate optional scalar code for tests.
-../flatc --rust --lobster optional_scalars.fbs
+../flatc --kotlin --rust --lobster optional_scalars.fbs
 
 # Generate the schema evolution tests
 ../flatc --cpp --scoped-enums $TEST_CPP_FLAGS -o evolution_test ./evolution_test/evolution_v*.fbs
diff --git a/tests/optional_scalars/ScalarStuff.kt b/tests/optional_scalars/ScalarStuff.kt
new file mode 100644
index 00000000..1d71b232
--- /dev/null
+++ b/tests/optional_scalars/ScalarStuff.kt
@@ -0,0 +1,268 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+package optional_scalars
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class ScalarStuff : Table() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : ScalarStuff {
+        __init(_i, _bb)
+        return this
+    }
+    val justI8 : Byte
+        get() {
+            val o = __offset(4)
+            return if(o != 0) bb.get(o + bb_pos) else 0
+        }
+    val maybeI8 : Byte?
+        get() {
+            val o = __offset(6)
+            return if(o != 0) bb.get(o + bb_pos) else null
+        }
+    val defaultI8 : Byte
+        get() {
+            val o = __offset(8)
+            return if(o != 0) bb.get(o + bb_pos) else 42
+        }
+    val justU8 : UByte
+        get() {
+            val o = __offset(10)
+            return if(o != 0) bb.get(o + bb_pos).toUByte() else 0u
+        }
+    val maybeU8 : UByte?
+        get() {
+            val o = __offset(12)
+            return if(o != 0) bb.get(o + bb_pos).toUByte() else null
+        }
+    val defaultU8 : UByte
+        get() {
+            val o = __offset(14)
+            return if(o != 0) bb.get(o + bb_pos).toUByte() else 42u
+        }
+    val justI16 : Short
+        get() {
+            val o = __offset(16)
+            return if(o != 0) bb.getShort(o + bb_pos) else 0
+        }
+    val maybeI16 : Short?
+        get() {
+            val o = __offset(18)
+            return if(o != 0) bb.getShort(o + bb_pos) else null
+        }
+    val defaultI16 : Short
+        get() {
+            val o = __offset(20)
+            return if(o != 0) bb.getShort(o + bb_pos) else 42
+        }
+    val justU16 : UShort
+        get() {
+            val o = __offset(22)
+            return if(o != 0) bb.getShort(o + bb_pos).toUShort() else 0u
+        }
+    val maybeU16 : UShort?
+        get() {
+            val o = __offset(24)
+            return if(o != 0) bb.getShort(o + bb_pos).toUShort() else null
+        }
+    val defaultU16 : UShort
+        get() {
+            val o = __offset(26)
+            return if(o != 0) bb.getShort(o + bb_pos).toUShort() else 42u
+        }
+    val justI32 : Int
+        get() {
+            val o = __offset(28)
+            return if(o != 0) bb.getInt(o + bb_pos) else 0
+        }
+    val maybeI32 : Int?
+        get() {
+            val o = __offset(30)
+            return if(o != 0) bb.getInt(o + bb_pos) else null
+        }
+    val defaultI32 : Int
+        get() {
+            val o = __offset(32)
+            return if(o != 0) bb.getInt(o + bb_pos) else 42
+        }
+    val justU32 : UInt
+        get() {
+            val o = __offset(34)
+            return if(o != 0) bb.getInt(o + bb_pos).toUInt() else 0u
+        }
+    val maybeU32 : UInt?
+        get() {
+            val o = __offset(36)
+            return if(o != 0) bb.getInt(o + bb_pos).toUInt() else null
+        }
+    val defaultU32 : UInt
+        get() {
+            val o = __offset(38)
+            return if(o != 0) bb.getInt(o + bb_pos).toUInt() else 42u
+        }
+    val justI64 : Long
+        get() {
+            val o = __offset(40)
+            return if(o != 0) bb.getLong(o + bb_pos) else 0L
+        }
+    val maybeI64 : Long?
+        get() {
+            val o = __offset(42)
+            return if(o != 0) bb.getLong(o + bb_pos) else null
+        }
+    val defaultI64 : Long
+        get() {
+            val o = __offset(44)
+            return if(o != 0) bb.getLong(o + bb_pos) else 42L
+        }
+    val justU64 : ULong
+        get() {
+            val o = __offset(46)
+            return if(o != 0) bb.getLong(o + bb_pos).toULong() else 0UL
+        }
+    val maybeU64 : ULong?
+        get() {
+            val o = __offset(48)
+            return if(o != 0) bb.getLong(o + bb_pos).toULong() else null
+        }
+    val defaultU64 : ULong
+        get() {
+            val o = __offset(50)
+            return if(o != 0) bb.getLong(o + bb_pos).toULong() else 42UL
+        }
+    val justF32 : Float
+        get() {
+            val o = __offset(52)
+            return if(o != 0) bb.getFloat(o + bb_pos) else 0.0f
+        }
+    val maybeF32 : Float?
+        get() {
+            val o = __offset(54)
+            return if(o != 0) bb.getFloat(o + bb_pos) else null
+        }
+    val defaultF32 : Float
+        get() {
+            val o = __offset(56)
+            return if(o != 0) bb.getFloat(o + bb_pos) else 42.0f
+        }
+    val justF64 : Double
+        get() {
+            val o = __offset(58)
+            return if(o != 0) bb.getDouble(o + bb_pos) else 0.0
+        }
+    val maybeF64 : Double?
+        get() {
+            val o = __offset(60)
+            return if(o != 0) bb.getDouble(o + bb_pos) else null
+        }
+    val defaultF64 : Double
+        get() {
+            val o = __offset(62)
+            return if(o != 0) bb.getDouble(o + bb_pos) else 42.0
+        }
+    val justBool : Boolean
+        get() {
+            val o = __offset(64)
+            return if(o != 0) 0.toByte() != bb.get(o + bb_pos) else false
+        }
+    val maybeBool : Boolean?
+        get() {
+            val o = __offset(66)
+            return if(o != 0) 0.toByte() != bb.get(o + bb_pos) else null
+        }
+    val defaultBool : Boolean
+        get() {
+            val o = __offset(68)
+            return if(o != 0) 0.toByte() != bb.get(o + bb_pos) else true
+        }
+    companion object {
+        fun validateVersion() = Constants.FLATBUFFERS_1_12_0()
+        fun getRootAsScalarStuff(_bb: ByteBuffer): ScalarStuff = getRootAsScalarStuff(_bb, ScalarStuff())
+        fun getRootAsScalarStuff(_bb: ByteBuffer, obj: ScalarStuff): ScalarStuff {
+            _bb.order(ByteOrder.LITTLE_ENDIAN)
+            return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb))
+        }
+        fun createScalarStuff(builder: FlatBufferBuilder, justI8: Byte, maybeI8: Byte?, defaultI8: Byte, justU8: UByte, maybeU8: UByte?, defaultU8: UByte, justI16: Short, maybeI16: Short?, defaultI16: Short, justU16: UShort, maybeU16: UShort?, defaultU16: UShort, justI32: Int, maybeI32: Int?, defaultI32: Int, justU32: UInt, maybeU32: UInt?, defaultU32: UInt, justI64: Long, maybeI64: Long?, defaultI64: Long, justU64: ULong, maybeU64: ULong?, defaultU64: ULong, justF32: Float, maybeF32: Float?, defaultF32: Float, justF64: Double, maybeF64: Double?, defaultF64: Double, justBool: Boolean, maybeBool: Boolean?, defaultBool: Boolean) : Int {
+            builder.startTable(33)
+            addDefaultF64(builder, defaultF64)
+            maybeF64?.run { addMaybeF64(builder, maybeF64) }
+            addJustF64(builder, justF64)
+            addDefaultU64(builder, defaultU64)
+            maybeU64?.run { addMaybeU64(builder, maybeU64) }
+            addJustU64(builder, justU64)
+            addDefaultI64(builder, defaultI64)
+            maybeI64?.run { addMaybeI64(builder, maybeI64) }
+            addJustI64(builder, justI64)
+            addDefaultF32(builder, defaultF32)
+            maybeF32?.run { addMaybeF32(builder, maybeF32) }
+            addJustF32(builder, justF32)
+            addDefaultU32(builder, defaultU32)
+            maybeU32?.run { addMaybeU32(builder, maybeU32) }
+            addJustU32(builder, justU32)
+            addDefaultI32(builder, defaultI32)
+            maybeI32?.run { addMaybeI32(builder, maybeI32) }
+            addJustI32(builder, justI32)
+            addDefaultU16(builder, defaultU16)
+            maybeU16?.run { addMaybeU16(builder, maybeU16) }
+            addJustU16(builder, justU16)
+            addDefaultI16(builder, defaultI16)
+            maybeI16?.run { addMaybeI16(builder, maybeI16) }
+            addJustI16(builder, justI16)
+            addDefaultBool(builder, defaultBool)
+            maybeBool?.run { addMaybeBool(builder, maybeBool) }
+            addJustBool(builder, justBool)
+            addDefaultU8(builder, defaultU8)
+            maybeU8?.run { addMaybeU8(builder, maybeU8) }
+            addJustU8(builder, justU8)
+            addDefaultI8(builder, defaultI8)
+            maybeI8?.run { addMaybeI8(builder, maybeI8) }
+            addJustI8(builder, justI8)
+            return endScalarStuff(builder)
+        }
+        fun startScalarStuff(builder: FlatBufferBuilder) = builder.startTable(33)
+        fun addJustI8(builder: FlatBufferBuilder, justI8: Byte) = builder.addByte(0, justI8, 0)
+        fun addMaybeI8(builder: FlatBufferBuilder, maybeI8: Byte) = builder.addByte(1, maybeI8, 0)
+        fun addDefaultI8(builder: FlatBufferBuilder, defaultI8: Byte) = builder.addByte(2, defaultI8, 42)
+        fun addJustU8(builder: FlatBufferBuilder, justU8: UByte) = builder.addByte(3, justU8.toByte(), 0)
+        fun addMaybeU8(builder: FlatBufferBuilder, maybeU8: UByte) = builder.addByte(4, maybeU8.toByte(), 0)
+        fun addDefaultU8(builder: FlatBufferBuilder, defaultU8: UByte) = builder.addByte(5, defaultU8.toByte(), 42)
+        fun addJustI16(builder: FlatBufferBuilder, justI16: Short) = builder.addShort(6, justI16, 0)
+        fun addMaybeI16(builder: FlatBufferBuilder, maybeI16: Short) = builder.addShort(7, maybeI16, 0)
+        fun addDefaultI16(builder: FlatBufferBuilder, defaultI16: Short) = builder.addShort(8, defaultI16, 42)
+        fun addJustU16(builder: FlatBufferBuilder, justU16: UShort) = builder.addShort(9, justU16.toShort(), 0)
+        fun addMaybeU16(builder: FlatBufferBuilder, maybeU16: UShort) = builder.addShort(10, maybeU16.toShort(), 0)
+        fun addDefaultU16(builder: FlatBufferBuilder, defaultU16: UShort) = builder.addShort(11, defaultU16.toShort(), 42)
+        fun addJustI32(builder: FlatBufferBuilder, justI32: Int) = builder.addInt(12, justI32, 0)
+        fun addMaybeI32(builder: FlatBufferBuilder, maybeI32: Int) = builder.addInt(13, maybeI32, 0)
+        fun addDefaultI32(builder: FlatBufferBuilder, defaultI32: Int) = builder.addInt(14, defaultI32, 42)
+        fun addJustU32(builder: FlatBufferBuilder, justU32: UInt) = builder.addInt(15, justU32.toInt(), 0)
+        fun addMaybeU32(builder: FlatBufferBuilder, maybeU32: UInt) = builder.addInt(16, maybeU32.toInt(), 0)
+        fun addDefaultU32(builder: FlatBufferBuilder, defaultU32: UInt) = builder.addInt(17, defaultU32.toInt(), 42)
+        fun addJustI64(builder: FlatBufferBuilder, justI64: Long) = builder.addLong(18, justI64, 0L)
+        fun addMaybeI64(builder: FlatBufferBuilder, maybeI64: Long) = builder.addLong(19, maybeI64, 0)
+        fun addDefaultI64(builder: FlatBufferBuilder, defaultI64: Long) = builder.addLong(20, defaultI64, 42L)
+        fun addJustU64(builder: FlatBufferBuilder, justU64: ULong) = builder.addLong(21, justU64.toLong(), 0)
+        fun addMaybeU64(builder: FlatBufferBuilder, maybeU64: ULong) = builder.addLong(22, maybeU64.toLong(), 0)
+        fun addDefaultU64(builder: FlatBufferBuilder, defaultU64: ULong) = builder.addLong(23, defaultU64.toLong(), 42)
+        fun addJustF32(builder: FlatBufferBuilder, justF32: Float) = builder.addFloat(24, justF32, 0.0)
+        fun addMaybeF32(builder: FlatBufferBuilder, maybeF32: Float) = builder.addFloat(25, maybeF32, 0.0)
+        fun addDefaultF32(builder: FlatBufferBuilder, defaultF32: Float) = builder.addFloat(26, defaultF32, 42.0)
+        fun addJustF64(builder: FlatBufferBuilder, justF64: Double) = builder.addDouble(27, justF64, 0.0)
+        fun addMaybeF64(builder: FlatBufferBuilder, maybeF64: Double) = builder.addDouble(28, maybeF64, 0.0)
+        fun addDefaultF64(builder: FlatBufferBuilder, defaultF64: Double) = builder.addDouble(29, defaultF64, 42.0)
+        fun addJustBool(builder: FlatBufferBuilder, justBool: Boolean) = builder.addBoolean(30, justBool, false)
+        fun addMaybeBool(builder: FlatBufferBuilder, maybeBool: Boolean) = builder.addBoolean(31, maybeBool, false)
+        fun addDefaultBool(builder: FlatBufferBuilder, defaultBool: Boolean) = builder.addBoolean(32, defaultBool, true)
+        fun endScalarStuff(builder: FlatBufferBuilder) : Int {
+            val o = builder.endTable()
+            return o
+        }
+    }
+}
diff --git a/tests/test.cpp b/tests/test.cpp
index 68f982b5..7f3c7d34 100644
--- a/tests/test.cpp
+++ b/tests/test.cpp
@@ -3466,6 +3466,7 @@ void OptionalScalarsTest() {
   const int kNumLanguages = 17;
   const auto supported = (flatbuffers::IDLOptions::kRust |
                           flatbuffers::IDLOptions::kSwift |
+                          flatbuffers::IDLOptions::kKotlin |
                           flatbuffers::IDLOptions::kLobster);
   for (int lang=0; lang<kNumLanguages; lang++) {
     flatbuffers::IDLOptions opts;