1 files changed, 29 insertions, 0 deletions
diff --git a/runtime/commonMain/src/kotlinx/serialization/json/internal/WriteMode.kt b/runtime/commonMain/src/kotlinx/serialization/json/internal/WriteMode.kt
new file mode 100644
index 00000000..e87a08da
--- /dev/null
+++ b/runtime/commonMain/src/kotlinx/serialization/json/internal/WriteMode.kt
@@ -0,0 +1,29 @@
+package kotlinx.serialization.json.internal
+
+import kotlinx.serialization.*
+import kotlin.jvm.*
+
+internal enum class WriteMode(@JvmField val begin: Char, @JvmField val end: Char) {
+    OBJ(BEGIN_OBJ, END_OBJ),
+    LIST(BEGIN_LIST, END_LIST),
+    MAP(BEGIN_OBJ, END_OBJ),
+    POLY_OBJ(BEGIN_LIST, END_LIST);
+
+    @JvmField
+    val beginTc: Byte = charToTokenClass(begin)
+    @JvmField
+    val endTc: Byte = charToTokenClass(end)
+}
+
+internal fun switchMode(desc: SerialDescriptor, typeParams: Array<out KSerializer<*>>): WriteMode =
+    when (desc.kind) {
+        UnionKind.POLYMORPHIC -> WriteMode.POLY_OBJ
+        StructureKind.LIST -> WriteMode.LIST
+        StructureKind.MAP -> {
+            val keyKind = typeParams[0].descriptor.kind
+            if (keyKind is PrimitiveKind || keyKind == UnionKind.ENUM_KIND)
+                WriteMode.MAP
+            else WriteMode.LIST
+        }
+        else -> WriteMode.OBJ
+    }