(#1533) More variance on some generics

src/main/java/org/cactoos/scalar/Flattened.java

@@ -38,7 +38,7 @@ public final class Flattened<X> extends ScalarEnvelope<X> {
      * Ctor.
      * @param sclr The func
      */
-    public Flattened(final Scalar<Scalar<X>> sclr) {
+    public Flattened(final Scalar<? extends Scalar<? extends X>> sclr) {
         super(() -> sclr.value().value());
     }
 }

src/main/java/org/cactoos/scalar/Folded.java

@@ -39,7 +39,7 @@ public final class Folded<X, T> implements Scalar<X> {
     /**
      * Original iterable.
      */
-    private final Iterable<T> iterable;
+    private final Iterable<? extends T> iterable;
 
     /**
      * Input.
@@ -49,31 +49,31 @@ public final class Folded<X, T> implements Scalar<X> {
     /**
      * Func.
      */
-    private final BiFunc<X, T, X> func;
+    private final BiFunc<? super X, ? super T, ? extends X> func;
 
     /**
      * Ctor.
      * @param ipt Input
      * @param fnc Func original
-     * @param list List of items
+     * @param list Array of items
      */
-    public Folded(final X ipt, final BiFunc<X, T, X> fnc,
-        final Iterable<T> list) {
-        this.iterable = list;
-        this.input = ipt;
-        this.func = fnc;
+    @SafeVarargs
+    public Folded(final X ipt, final BiFunc<? super X, ? super T, ? extends X> fnc,
+        final T... list) {
+        this(ipt, fnc, new IterableOf<>(list));
     }
 
     /**
      * Ctor.
      * @param ipt Input
      * @param fnc Func original
-     * @param list Array of items
+     * @param list List of items
      */
-    @SafeVarargs
-    public Folded(final X ipt, final BiFunc<X, T, X> fnc,
-        final T... list) {
-        this(ipt, fnc, new IterableOf<>(list));
+    public Folded(final X ipt, final BiFunc<? super X, ? super T, ? extends X> fnc,
+        final Iterable<? extends T> list) {
+        this.iterable = list;
+        this.input = ipt;
+        this.func = fnc;
     }
 
     @Override

src/main/java/org/cactoos/scalar/HighestOf.java

@@ -56,12 +56,7 @@
  * @see IoChecked
  * @since 0.29
  */
-public final class HighestOf<T extends Comparable<T>> implements Scalar<T> {
-
-    /**
-     * Result.
-     */
-    private final Scalar<T> result;
+public final class HighestOf<T extends Comparable<? super T>> extends ScalarEnvelope<T> {
 
     /**
      * Ctor.
@@ -82,31 +77,28 @@ public HighestOf(final T... items) {
      * @param scalars The scalars
      */
     @SafeVarargs
-    public HighestOf(final Scalar<T>... scalars) {
+    public HighestOf(final Scalar<? extends T>... scalars) {
         this(new IterableOf<>(scalars));
     }
 
     /**
      * Ctor.
      * @param iterable The items
      */
-    public HighestOf(final Iterable<Scalar<T>> iterable) {
-        this.result = new Reduced<>(
-            (first, second) -> {
-                final T value;
-                if (first.compareTo(second) > 0) {
-                    value = first;
-                } else {
-                    value = second;
-                }
-                return value;
-            },
-            iterable
+    public HighestOf(final Iterable<? extends Scalar<? extends T>> iterable) {
+        super(
+            new Reduced<>(
+                (first, second) -> {
+                    final T value;
+                    if (first.compareTo(second) > 0) {
+                        value = first;
+                    } else {
+                        value = second;
+                    }
+                    return value;
+                },
+                iterable
+            )
         );
     }
-
-    @Override
-    public T value() throws Exception {
-        return this.result.value();
-    }
 }

src/main/java/org/cactoos/scalar/LowestOf.java

@@ -56,13 +56,7 @@
  * @see IoChecked
  * @since 0.29
  */
-public final class LowestOf<T extends Comparable<T>> implements Scalar<T> {
-
-    /**
-     * Result.
-     */
-    private final Scalar<T> result;
-
+public final class LowestOf<T extends Comparable<? super T>> extends ScalarEnvelope<T> {
     /**
      * Ctor.
      * @param items The comparable items
@@ -82,31 +76,28 @@ public LowestOf(final T... items) {
      * @param scalars The scalars
      */
     @SafeVarargs
-    public LowestOf(final Scalar<T>... scalars) {
+    public LowestOf(final Scalar<? extends T>... scalars) {
         this(new IterableOf<>(scalars));
     }
 
     /**
      * Ctor.
      * @param iterable The items
      */
-    public LowestOf(final Iterable<Scalar<T>> iterable) {
-        this.result = new Reduced<>(
-            (first, second) -> {
-                final T value;
-                if (first.compareTo(second) < 0) {
-                    value = first;
-                } else {
-                    value = second;
-                }
-                return value;
-            },
-            iterable
+    public LowestOf(final Iterable<? extends Scalar<? extends T>> iterable) {
+        super(
+            new Reduced<>(
+                (first, second) -> {
+                    final T value;
+                    if (first.compareTo(second) < 0) {
+                        value = first;
+                    } else {
+                        value = second;
+                    }
+                    return value;
+                },
+                iterable
+            )
         );
     }
-
-    @Override
-    public T value() throws Exception {
-        return this.result.value();
-    }
 }

src/main/java/org/cactoos/scalar/Reduced.java

@@ -77,42 +77,42 @@ public final class Reduced<T> implements Scalar<T> {
     /**
      * Items.
      */
-    private final Iterable<Scalar<T>> items;
+    private final Iterable<? extends Scalar<? extends T>> items;
 
     /**
      * Folding function.
      */
-    private final BiFunc<T, T, T> function;
+    private final BiFunc<? super T, ? super T, ? extends T> function;
 
     /**
      * Ctor.
      * @param reduce Reducing function
-     * @param scalars The scalars
+     * @param values Values to be wrapped as scalars
      */
+    @SafeVarargs
     public Reduced(
-        final BiFunc<T, T, T> reduce,
-        final Iterable<Scalar<T>> scalars
+        final BiFunc<? super T, ? super T, ? extends T> reduce,
+        final T... values
     ) {
-        this.items = scalars;
-        this.function = reduce;
+        this(reduce, new Mapped<>(Constant::new, values));
     }
 
     /**
      * Ctor.
      * @param reduce Reducing function
-     * @param values Values to be wrapped as scalars
+     * @param scalars The scalars
      */
-    @SafeVarargs
     public Reduced(
-        final BiFunc<T, T, T> reduce,
-        final T... values
+        final BiFunc<? super T, ? super T, ? extends T> reduce,
+        final Iterable<? extends Scalar<? extends T>> scalars
     ) {
-        this(reduce, new Mapped<>(Constant::new, values));
+        this.items = scalars;
+        this.function = reduce;
     }
 
     @Override
     public T value() throws Exception {
-        final Iterator<Scalar<T>> iter = this.items.iterator();
+        final Iterator<? extends Scalar<? extends T>> iter = this.items.iterator();
         if (!iter.hasNext()) {
             throw new NoSuchElementException(
                 "Can't find first element in an empty iterable"