Added Cached Version of scalar

src/main/java/org/cactoos/func/CachedScalar.java

@@ -0,0 +1,69 @@
+/**
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017 Yegor Bugayenko
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package org.cactoos.func;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import org.cactoos.Scalar;
+
+/**
+ * Cached version of a Scalar.
+ *
+ * <p>There is no thread-safety guarantee.
+ *
+ * @author Tim Hinkes ([email protected])
+ * @version $Id$
+ * @param <T> Type of result
+ * @since 0.3
+ */
+public final class CachedScalar<T> implements Scalar<T> {
+
+    /**
+     * The scalar to cache.
+     */
+    private final Scalar<T> source;
+
+    /**
+     * The list used as a optional value.
+     */
+    private final List<T> cache;
+
+    /**
+     * Ctor.
+     * @param source The Scalar to cache
+     */
+    public CachedScalar(final Scalar<T> source) {
+        this.source = source;
+        this.cache = new ArrayList<>(1);
+    }
+
+    @Override
+    public T asValue() throws IOException {
+        if (this.cache.isEmpty()) {
+            this.cache.add(this.source.asValue());
+        }
+        return this.cache.get(0);
+    }
+}