Kotlin newInstance() Fragment pattern

Argument.kt

/**
 * Eases the Fragment.newInstance ceremony by marking the fragment's args with this delegate
 * Just write the property in newInstance and read it like any other property after the fragment has been created
 *
 * Inspired by Adam Powell, he mentioned it during his IO/17 talk about Kotlin
 */
class Argument<T : Any> : kotlin.properties.ReadWriteProperty<Fragment, T>
{
	var value: T? = null

	override operator fun getValue(thisRef: android.support.v4.app.Fragment, property: kotlin.reflect.KProperty<*>): T
	{
		if(value == null)
		{
			val args = thisRef.arguments ?: throw IllegalStateException(
				"Cannot read property ${property.name} if no arguments have been set")
			@Suppress("UNCHECKED_CAST")
			value = args.get(property.name) as T
		}
		return value ?: throw IllegalStateException("Property ${property.name} could not be read")
	}

	override operator fun setValue(thisRef: android.support.v4.app.Fragment, property: kotlin.reflect.KProperty<*>, value: T)
	{
		if(thisRef.arguments == null) thisRef.arguments = android.os.Bundle()

		val args = thisRef.arguments
		args?.let {
			val key = property.name

			when(value)
			{
				is String                -> args.putString(key, value)
				is Int                   -> args.putInt(key, value)
				is Short                 -> args.putShort(key, value)
				is Long                  -> args.putLong(key, value)
				is Byte                  -> args.putByte(key, value)
				is ByteArray             -> args.putByteArray(key, value)
				is Char                  -> args.putChar(key, value)
				is CharArray             -> args.putCharArray(key, value)
				is CharSequence          -> args.putCharSequence(key, value)
				is Float                 -> args.putFloat(key, value)
				is Bundle -> args.putBundle(key, value)
				is Binder -> BundleCompat.putBinder(args, key, value)
				is android.os.Parcelable -> args.putParcelable(key, value)
				is java.io.Serializable  -> args.putSerializable(key, value)
				else                     -> throw IllegalStateException(
					"Type ${value.javaClass.name} of property ${property.name} is not supported")
			}
		}
	}
}

class NullableArgument<T> : kotlin.properties.ReadWriteProperty<Fragment, T?>
{
	var value: T? = null

	override operator fun getValue(thisRef: android.support.v4.app.Fragment, property: kotlin.reflect.KProperty<*>): T?
	{
		// If the fragment does not have any arguments, we assume that no properties were provided
		if(thisRef.arguments == null)
		{
			return null
		}

		if(value == null)
		{
			val args = thisRef.arguments ?: throw IllegalStateException(
				"Cannot read property ${property.name} if no arguments have been set")
			@Suppress("UNCHECKED_CAST")
			value = args.get(property.name) as T?
		}
		return value
	}

	override operator fun setValue(thisRef: android.support.v4.app.Fragment, property: kotlin.reflect.KProperty<*>, value: T?)
	{
		if(value == null)
		{
			return
		}

		if(thisRef.arguments == null) thisRef.arguments = android.os.Bundle()

		val args = thisRef.arguments
		args?.let {
			val key = property.name

			when(value)
			{
				is String                -> args.putString(key, value)
				is Int                   -> args.putInt(key, value)
				is Short                 -> args.putShort(key, value)
				is Long                  -> args.putLong(key, value)
				is Byte                  -> args.putByte(key, value)
				is ByteArray             -> args.putByteArray(key, value)
				is Char                  -> args.putChar(key, value)
				is CharArray             -> args.putCharArray(key, value)
				is CharSequence          -> args.putCharSequence(key, value)
				is Float                 -> args.putFloat(key, value)
				is Bundle -> args.putBundle(key, value)
				is Binder -> BundleCompat.putBinder(args, key, value)
				is android.os.Parcelable -> args.putParcelable(key, value)
				is java.io.Serializable  -> args.putSerializable(key, value)
				is Any                   -> throw IllegalStateException(
					"Type ${value.javaClass.name} of property ${property.name} is not supported")
				else                     -> throw IllegalStateException(
					"Property ${property.name} is not supported")
			}
		}
	}
}