[isis] 07/11: ISIS-898 Internal API: introduces _Lazy a memoizing supplier

[ah...@apache.org]

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ahuber pushed a commit to branch dev/2.0.0/ISIS-898-treeview
in repository https://gitbox.apache.org/repos/asf/isis.git

commit 28f1b610e3182404d1d83ef1a816738a2e44f2a0
Author: Andi Huber <ah...@apache.org>
AuthorDate: Mon Apr 16 08:17:56 2018 +0200

    ISIS-898 Internal API: introduces _Lazy a memoizing supplier
---
 .../apache/isis/applib/internal/base/_Lazy.java    | 79 ++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/core/applib/src/main/java/org/apache/isis/applib/internal/base/_Lazy.java b/core/applib/src/main/java/org/apache/isis/applib/internal/base/_Lazy.java
new file mode 100644
index 0000000..802ec57
--- /dev/null
+++ b/core/applib/src/main/java/org/apache/isis/applib/internal/base/_Lazy.java
@@ -0,0 +1,79 @@
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you 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 org.apache.isis.applib.internal.base;
+
+import java.util.Objects;
+import java.util.function.Supplier;
+
+/**
+ * <h1>- internal use only -</h1>
+ * <p>
+ * Supplier with memoization.
+ * </p>
+ * <p>
+ * <b>WARNING</b>: Do <b>NOT</b> use any of the classes provided by this package! <br/> 
+ * These may be changed or removed without notice!
+ * </p>
+ * 
+ * @since 2.0.0
+ */
+public final class _Lazy<T> implements Supplier<T> {
+
+	private final Supplier<? extends T> supplier;
+	private T value;
+	private boolean memoized;
+
+	public static <T> _Lazy<T> of(Supplier<? extends T> supplier) {
+		return new _Lazy<T>(supplier);
+	}
+	
+	private _Lazy(Supplier<? extends T> supplier) {
+		Objects.requireNonNull(supplier, "supplier required");
+		this.supplier = supplier;
+	}
+
+	public boolean isMemoized() {
+		return memoized;
+	}
+
+	/**
+	 * Clears the lazy's memoized value. Resets this lazy to its initial state.<br> 
+	 * isMemoized() = false;
+	 * 
+	 */
+	public void clear() {
+		this.memoized = false;
+		this.value = null;
+	}
+
+	/**
+	 * Evaluates this lazy value and memoizes it, when called the first time 
+	 * after initialization or clear().
+	 */
+	@Override
+	public T get() {
+		if(memoized) {
+			return value;
+		}
+		memoized=true;
+		return value = supplier.get();
+	}
+
+}

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