Introduce ReflectProperties for lazy weak/soft property delegates

This class needs to be written in Java because no Kotlin classes can be used in
KClassImpl constructor (otherwise since each Kotlin class creates a KClassImpl
in its static initializer, this would result in infinite recursion)

core/reflection.jvm/src/kotlin/reflect/jvm/internal/ReflectProperties.java

@@ -0,0 +1,132 @@
+/*
+ * Copyright 2010-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kotlin.reflect.jvm.internal;
+
+import kotlin.Function0;
+import org.jetbrains.annotations.NotNull;
+
+import java.lang.ref.SoftReference;
+import java.lang.ref.WeakReference;
+
+/* package */ class ReflectProperties {
+    public static abstract class Val<T> {
+        private static final Object NULL_VALUE = new Object() {};
+
+        public abstract T get(Object instance, Object metadata);
+
+        protected Object escape(T value) {
+            return value == null ? NULL_VALUE : value;
+        }
+
+        @SuppressWarnings("unchecked")
+        protected T unescape(Object value) {
+            return value == NULL_VALUE ? null : (T) value;
+        }
+    }
+
+    // A delegate for a lazy property, whose initializer may be invoked multiple times including simultaneously from different threads
+    public static class LazyVal<T> extends Val<T> {
+        private final Function0<T> initializer;
+        private Object value = null;
+
+        public LazyVal(@NotNull Function0<T> initializer) {
+            this.initializer = initializer;
+        }
+
+        @Override
+        public T get(Object instance, Object metadata) {
+            Object cached = value;
+            if (cached != null) {
+                return unescape(cached);
+            }
+
+            T result = initializer.invoke();
+            value = escape(result);
+
+            return result;
+        }
+    }
+
+    // A delegate for a lazy property on a soft reference, whose initializer may be invoked multiple times
+    // including simultaneously from different threads
+    public static class LazySoftVal<T> extends Val<T> {
+        private final Function0<T> initializer;
+        private SoftReference<Object> value = null;
+
+        public LazySoftVal(@NotNull Function0<T> initializer) {
+            this.initializer = initializer;
+        }
+
+        @Override
+        public T get(Object instance, Object metadata) {
+            SoftReference<Object> cached = value;
+            if (cached != null) {
+                Object result = cached.get();
+                if (result != null) {
+                    return unescape(result);
+                }
+            }
+
+            T result = initializer.invoke();
+            value = new SoftReference<Object>(escape(result));
+
+            return result;
+        }
+    }
+
+    // A delegate for a lazy property on a weak reference, whose initializer may be invoked multiple times
+    // including simultaneously from different threads
+    public static class LazyWeakVal<T> extends Val<T> {
+        private final Function0<T> initializer;
+        private WeakReference<Object> value = null;
+
+        public LazyWeakVal(@NotNull Function0<T> initializer) {
+            this.initializer = initializer;
+        }
+
+        @Override
+        public T get(Object instance, Object metadata) {
+            WeakReference<Object> cached = value;
+            if (cached != null) {
+                Object result = cached.get();
+                if (result != null) {
+                    return unescape(result);
+                }
+            }
+
+            T result = initializer.invoke();
+            value = new WeakReference<Object>(escape(result));
+
+            return result;
+        }
+    }
+
+    @NotNull
+    public static <T> LazyVal<T> lazy(@NotNull Function0<T> initializer) {
+        return new LazyVal<T>(initializer);
+    }
+
+    @NotNull
+    public static <T> LazySoftVal<T> lazySoft(@NotNull Function0<T> initializer) {
+        return new LazySoftVal<T>(initializer);
+    }
+
+    @NotNull
+    public static <T> LazyWeakVal<T> lazyWeak(@NotNull Function0<T> initializer) {
+        return new LazyWeakVal<T>(initializer);
+    }
+}