1 files changed, 38 insertions, 0 deletions
diff --git a/src/main/kotlin/util/MutableMapWithMaxSize.kt b/src/main/kotlin/util/MutableMapWithMaxSize.kt
new file mode 100644
index 0000000..067e652
--- /dev/null
+++ b/src/main/kotlin/util/MutableMapWithMaxSize.kt
@@ -0,0 +1,38 @@
+
+package moe.nea.firmament.util
+
+fun <K, V> mutableMapWithMaxSize(maxSize: Int): MutableMap<K, V> = object : LinkedHashMap<K, V>() {
+    override fun removeEldestEntry(eldest: MutableMap.MutableEntry<K, V>): Boolean {
+        return size > maxSize
+    }
+}
+
+fun <T, R> ((T) -> R).memoizeIdentity(maxCacheSize: Int): (T) -> R {
+    val memoized = { it: IdentityCharacteristics<T> ->
+        this(it.value)
+    }.memoize(maxCacheSize)
+    return { memoized(IdentityCharacteristics(it)) }
+}
+
+@PublishedApi
+internal val SENTINEL_NULL = java.lang.Object()
+
+/**
+ * Requires the map to only contain values of type [R] or [SENTINEL_NULL]. This is ensured if the map is only ever
+ * accessed via this function.
+ */
+inline fun <T, R> MutableMap<T, Any>.computeNullableFunction(key: T, crossinline func: () -> R): R {
+    val value = this.getOrPut(key) {
+        func() ?: SENTINEL_NULL
+    }
+    @Suppress("UNCHECKED_CAST")
+    return if (value === SENTINEL_NULL) null as R
+    else value as R
+}
+
+fun <T, R> ((T) -> R).memoize(maxCacheSize: Int): (T) -> R {
+    val map = mutableMapWithMaxSize<T, Any>(maxCacheSize)
+    return {
+        map.computeNullableFunction(it) { this@memoize(it) }
+    }
+}