Create shared state in EnhancedPlacementContext for memory efficiency

src/main/kotlin/ru/dbotthepony/mc/otm/worldgen/EnhancedPlacementContext.kt

@@ -1,5 +1,6 @@
 package ru.dbotthepony.mc.otm.worldgen
 
+import it.unimi.dsi.fastutil.objects.Reference2ObjectOpenHashMap
 import net.minecraft.core.BlockPos
 import net.minecraft.util.RandomSource
 import net.minecraft.world.level.ChunkPos
@@ -18,15 +19,32 @@ class EnhancedPlacementContext {
 		fun place(context: EnhancedPlacementContext, positions: List<BlockPos>, feature: EnhancedFeature.Configured<*, *>)
 	}
 
-	val level: WorldGenLevel
-	val generator: ChunkGenerator
-	val random: RandomSource
-	val origin: ChunkPos
-	private val placer: Placer
-	val vanillaContext: PlacementContext
+	private data class SharedState(
+		val level: WorldGenLevel,
+		val generator: ChunkGenerator,
+		val random: RandomSource,
+		val origin: ChunkPos,
+		val placer: Placer,
+		val vanillaContext: PlacementContext,
+	)
 
-	private var parent: EnhancedPlacementContext? = null
-	private val variables = HashMap<PlacementVariable<*>, KOptional<*>>()
+	private val state: SharedState
+
+	val level: WorldGenLevel
+		get() = state.level
+	val generator: ChunkGenerator
+		get() = state.generator
+	val random: RandomSource
+		get() = state.random
+	val origin: ChunkPos
+		get() = state.origin
+	private val placer: Placer
+		get() = state.placer
+	val vanillaContext: PlacementContext
+		get() = state.vanillaContext
+
+	private val parent: EnhancedPlacementContext?
+	private val variables = Reference2ObjectOpenHashMap<PlacementVariable<*>, KOptional<*>>(0)
 
 	private fun <T> recursiveGet(index: PlacementVariable<T>): KOptional<T>? {
 		return variables[index] as KOptional<T>? ?: parent?.recursiveGet(index)
@@ -56,23 +74,21 @@ class EnhancedPlacementContext {
 		origin: ChunkPos,
 		placer: Placer,
 	) {
-		this.level = level
-		this.generator = generator
-		this.random = random
-		this.origin = origin
-		this.placer = placer
+		state = SharedState(
+			level = level,
+			generator = generator,
+			random = random,
+			origin = origin,
+			placer = placer,
+			vanillaContext = PlacementContext(level, generator, Optional.empty())
+		)
 
-		vanillaContext = PlacementContext(level, generator, Optional.empty())
+		parent = null
 	}
 
 	private constructor(parent: EnhancedPlacementContext) {
-		this.level = parent.level
-		this.generator = parent.generator
-		this.random = parent.random
-		this.origin = parent.origin
-		this.placer = parent.placer
+		this.state = parent.state
 		this.parent = parent
-		this.vanillaContext = parent.vanillaContext
 	}
 
 	fun push(): EnhancedPlacementContext {