(yegor256#1572) Generify fnc parameter of FuncWithFallback

Co-authored-by: Victor Noël <[email protected]>

Author: DmitryBarskov

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

@@ -95,7 +95,7 @@ public final class FuncWithFallback<X, Y> implements Func<X, Y> {
     /**
      * The func.
      */
-    private final Func<X, Y> func;
+    private final Func<? super X, ? extends Y> func;
 
     /**
      * The fallbacks.
@@ -108,7 +108,8 @@ public final class FuncWithFallback<X, Y> implements Func<X, Y> {
      * @param fbks The fallbacks
      */
     @SafeVarargs
-    public FuncWithFallback(final Func<X, Y> fnc, final Fallback<? extends Y>... fbks) {
+    public FuncWithFallback(final Func<? super X, ? extends Y> fnc,
+        final Fallback<? extends Y>... fbks) {
         this(fnc, new IterableOf<>(fbks));
     }
 
@@ -117,9 +118,8 @@ public FuncWithFallback(final Func<X, Y> fnc, final Fallback<? extends Y>... fbk
      * @param fnc The func
      * @param fbks The fallbacks
      */
-    public FuncWithFallback(
-        final Func<X, Y> fnc, final Iterable<Fallback<? extends Y>> fbks
-    ) {
+    public FuncWithFallback(final Func<? super X, ? extends Y> fnc,
+        final Iterable<Fallback<? extends Y>> fbks) {
         this.func = fnc;
         this.fallbacks = fbks;
     }