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diff --git a/runtime/commonMain/src/kotlinx/serialization/ContextSerializer.kt b/runtime/commonMain/src/kotlinx/serialization/ContextSerializer.kt
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+++ b/runtime/commonMain/src/kotlinx/serialization/ContextSerializer.kt
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+/*
+ * Copyright 2017-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+@file:Suppress("RedundantVisibilityModifier")
+
+package kotlinx.serialization
+
+import kotlinx.serialization.internal.*
+import kotlinx.serialization.modules.*
+import kotlin.reflect.*
+
+/**
+ * This class provides support for retrieving a serializer in runtime, instead of using the one precompiled by the serialization plugin.
+ * This serializer is enabled by [ContextualSerialization].
+ *
+ * Typical usage of ContextSerializer would be a serialization of a class which does not have
+ * static serializer (e.g. Java class or class from 3rd party library);
+ * or desire to override serialized class form in one dedicated output format.
+ *
+ * Serializers are being looked for in a [SerialModule] from the target [Encoder] or [Decoder], using statically known [KClass].
+ * To create a serial module, use [SerializersModule] factory function.
+ * To pass it to encoder and decoder, refer to particular [SerialFormat]'s documentation.
+ *
+ */
+@ImplicitReflectionSerializer
+public class ContextSerializer<T : Any>(private val serializableClass: KClass<T>) : KSerializer<T> {
+    public override val descriptor: SerialDescriptor = object : SerialClassDescImpl("CONTEXT") {} // todo: remove this crutch
+
+    public override fun serialize(encoder: Encoder, obj: T) {
+        val s = encoder.context.getContextualOrDefault(obj)
+        encoder.encodeSerializableValue(s, obj)
+    }
+
+    public override fun deserialize(decoder: Decoder): T {
+        val s = decoder.context.getContextualOrDefault(serializableClass)
+        return decoder.decodeSerializableValue(s)
+    }
+}