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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 <ahu...@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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