Added usage of cachedScalar for size()

src/main/java/org/cactoos/list/IterableAsList.java

@@ -26,6 +26,8 @@
 import java.util.AbstractList;
 import java.util.ArrayList;
 import java.util.List;
+import org.cactoos.func.CachedScalar;
+import org.cactoos.func.UncheckedScalar;
 import org.cactoos.text.FormattedText;
 
 /**
@@ -52,12 +54,8 @@ public final class IterableAsList<T> extends AbstractList<T> {
 
     /**
      * Iterable length.
-     *
-     * @todo #39:30m Needs cached `LengthOfIterable` version
-     *  to improve `IterableAsList` performance. Now each call
-     *  to `size()` goes through all iterable to calculate the size.
      */
-    private final LengthOfIterable length;
+    private final UncheckedScalar<Integer> length;
 
     /**
      * Ctor.
@@ -68,7 +66,11 @@ public IterableAsList(final Iterable<T> iterable) {
         super();
         this.source = iterable;
         this.cache = new ArrayList<>(0);
-        this.length = new LengthOfIterable(iterable);
+        this.length = new UncheckedScalar<>(
+            new CachedScalar<>(
+                new LengthOfIterable(iterable)
+            )
+        );
     }
 
     @Override