(#1533) Exploit generic variance in package bytes

src/main/java/org/cactoos/bytes/CheckedBytes.java

@@ -43,14 +43,14 @@ public final class CheckedBytes<E extends Exception> implements Bytes {
     /**
      * Function that wraps exception of {@link #origin} to the required type.
      */
-    private final Func<Exception, E> func;
+    private final Func<? super Exception, ? extends E> func;
 
     /**
      * Ctor.
      * @param orig Origin bytes.
      * @param fnc Function that wraps exceptions.
      */
-    public CheckedBytes(final Bytes orig, final Func<Exception, E> fnc) {
+    public CheckedBytes(final Bytes orig, final Func<? super Exception, ? extends E> fnc) {
         this.origin = orig;
         this.func = fnc;
     }

src/main/java/org/cactoos/bytes/UncheckedBytes.java

@@ -44,7 +44,7 @@ public final class UncheckedBytes implements Bytes {
     /**
      * Fallback.
      */
-    private final Func<Exception, byte[]> fallback;
+    private final Func<? super Exception, byte[]> fallback;
 
     /**
      * Ctor.
@@ -67,7 +67,7 @@ public UncheckedBytes(final Bytes bts) {
      * @since 0.5
      */
     public UncheckedBytes(final Bytes bts,
-        final Func<Exception, byte[]> fbk) {
+        final Func<? super Exception, byte[]> fbk) {
         this.bytes = bts;
         this.fallback = fbk;
     }

src/main/java/org/cactoos/collection/package-info.java

@@ -26,5 +26,8 @@
  * Collections, tests.
  *
  * @since 0.14
+ * @todo #1533:30min Continue to exploit generic variance for package
+ *  org.cactoos.collection to ensure typing works as best as
+ *  possible as it is explained in #1533 issue.
  */
 package org.cactoos.collection;

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

@@ -44,20 +44,20 @@ public final class Checked<T, E extends Exception> implements Scalar<T> {
     /**
      * Function that wraps exception.
      */
-    private final Func<Exception, E> func;
+    private final Func<? super Exception, ? extends E> func;
 
     /**
      * Original scalar.
      */
-    private final Scalar<T> origin;
+    private final Scalar<? extends T> origin;
 
     /**
      * Ctor.
      * @param scalar Encapsulated scalar
      * @param fnc Func that wraps exception
      */
-    public Checked(final Scalar<T> scalar,
-        final Func<Exception, E> fnc) {
+    public Checked(final Scalar<? extends T> scalar,
+        final Func<? super Exception, ? extends E> fnc) {
         this.func = fnc;
         this.origin = scalar;
     }

src/test/java/org/cactoos/scalar/CheckedTest.java

@@ -25,9 +25,12 @@
 
 import java.io.FileNotFoundException;
 import java.io.IOException;
+import java.nio.channels.AcceptPendingException;
 import org.hamcrest.MatcherAssert;
 import org.hamcrest.Matchers;
+import org.hamcrest.core.IsEqual;
 import org.junit.Test;
+import org.llorllale.cactoos.matchers.Assertion;
 
 /**
  * Test case for {@link Checked}.
@@ -46,6 +49,30 @@ public void runtimeExceptionGoesOut() throws Exception {
         ).value();
     }
 
+    @Test(expected = IllegalStateException.class)
+    public void usesGenericVarianceOnExceptionTypes() throws Exception {
+        new Checked<String, IllegalStateException>(
+            () -> {
+                throw new IllegalStateException();
+            },
+            (Throwable ex) -> {
+                return new AcceptPendingException();
+            }
+        ).value();
+    }
+
+    @SuppressWarnings("PMD.AvoidDuplicateLiterals")
+    public void usesContravarianceOnResultType() throws Exception {
+        new Assertion<>(
+            "Must use contravariance on result",
+            new Checked<CharSequence, IOException>(
+                () -> new String("contravariance"),
+                IOException::new
+            ).value(),
+            new IsEqual<>("contravariance")
+        );
+    }
+
     @Test(expected = IOException.class)
     public void throwsIoException() throws Exception {
         new Checked<>(