Remove Tuple generic parameter

server/src/main/java/io/spine/server/tuple/Element.java

@@ -87,7 +87,7 @@ final class Element implements Serializable {
      * Obtains the value of the element by its index and casts it to the type {@code <T>}.
      */
     @SuppressWarnings("TypeParameterUnusedInFormals") // See Javadoc.
-    static <M extends Message, T> T value(Tuple<M> tuple, IndexOf index) {
+    static <M extends Message, T> T value(Tuple tuple, IndexOf index) {
         @SuppressWarnings("unchecked") // The caller is responsible for the correct type.
         var value = (T) tuple.get(index.value());
         return value;

server/src/main/java/io/spine/server/tuple/Pair.java

@@ -53,7 +53,7 @@
  *         the type of the second element
  */
 public final class Pair<A extends Message, B>
-        extends Tuple<A>
+        extends Tuple
         implements AValue<A>, BValue<B> {
 
     private static final long serialVersionUID = 0L;

server/src/main/java/io/spine/server/tuple/Quartet.java

@@ -58,7 +58,7 @@
  *         the type of the fourth element
  */
 public final class Quartet<A extends Message, B, C, D>
-        extends Tuple<A>
+        extends Tuple
         implements AValue<A>, BValue<B>, CValue<C>, DValue<D> {
 
     private static final long serialVersionUID = 0L;

server/src/main/java/io/spine/server/tuple/Quintet.java

@@ -61,8 +61,8 @@
  *         the type of the fifth element
  */
 public final class Quintet<A extends Message, B, C, D, E>
-    extends Tuple<A>
-    implements AValue<A>, BValue<B>, CValue<C>, DValue<D>, EValue<E> {
+        extends Tuple
+        implements AValue<A>, BValue<B>, CValue<C>, DValue<D>, EValue<E> {
 
     private static final long serialVersionUID = 0L;
 

server/src/main/java/io/spine/server/tuple/Triplet.java

@@ -55,7 +55,7 @@
  *         the type of the third element
  */
 public final class Triplet<A extends Message, B, C>
-        extends Tuple<A>
+        extends Tuple
         implements AValue<A>, BValue<B>, CValue<C> {
 
     private static final long serialVersionUID = 0L;

server/src/main/java/io/spine/server/tuple/Tuple.java

@@ -46,11 +46,8 @@
 
 /**
  * Abstract base for tuple classes.
- *
- * @param <M>
- *         the type of the tuple first element
  */
-public abstract class Tuple<M extends Message> implements Iterable<M>, Serializable {
+public abstract class Tuple implements Iterable<Message>, Serializable {
 
     private static final long serialVersionUID = 0L;
 
@@ -86,7 +83,7 @@ protected Tuple(Object... values) {
      * @throws IllegalArgumentException if the passed value is {@link Empty}
      */
     @CanIgnoreReturnValue
-    static <M extends Message, T extends Tuple<?>>
+    static <M extends Message, T extends Tuple>
     @Nullable M checkNotEmpty(Class<T> checkingClass, @Nullable M value) {
         if (value == null) {
             return null;
@@ -103,32 +100,32 @@ protected Tuple(Object... values) {
 
     @CanIgnoreReturnValue
     @SuppressWarnings("ConstantConditions") /* `checkNotNull` is used by design. */
-    static <M extends Message, T extends Tuple<?>>
+    static <M extends Message, T extends Tuple>
     M checkNotNullOrEmpty(Class<T> checkingClass, M value) {
         var result = checkNotEmpty(checkingClass, value);
         checkNotNull(result);
         return result;
     }
 
     @SafeVarargs
-    static <M extends Message, T extends Tuple<?>>
+    static <M extends Message, T extends Tuple>
     void checkAllNotNullOrEmpty(Class<T> checkingClass, M... values) {
         for (var value : values) {
             checkNotNullOrEmpty(checkingClass, value);
         }
     }
 
     @SafeVarargs
-    static <M extends Message, T extends Tuple<?>>
+    static <M extends Message, T extends Tuple>
     void checkAllNotEmpty(Class<T> checkingClass, M... values) {
         for (var value : values) {
             checkNotEmpty(checkingClass, value);
         }
     }
 
     @Override
-    public final @NonNull Iterator<M> iterator() {
-        Iterator<M> result = new ExtractingIterator<>(values);
+    public final @NonNull Iterator<Message> iterator() {
+        Iterator<Message> result = new ExtractingIterator(values);
         return result;
     }
 
@@ -158,7 +155,7 @@ public final boolean equals(Object obj) {
         if (!(obj instanceof Tuple)) {
             return false;
         }
-        var other = (Tuple<?>) obj;
+        var other = (Tuple) obj;
         return Objects.equals(this.values, other.values);
     }
 
@@ -178,12 +175,8 @@ static boolean isOptionalPresent(Object value) {
 
     /**
      * Traverses through elements obtaining a message value from them.
-     *
-     * @param <M>
-     *         the type of the messages extracted by the iterator
      */
-    private static final class ExtractingIterator<M extends Message>
-            extends UnmodifiableIterator<M> {
+    private static final class ExtractingIterator extends UnmodifiableIterator<Message> {
 
         private final Iterator<Element> source;
 
@@ -198,10 +191,9 @@ public boolean hasNext() {
         }
 
         @Override
-        public M next() {
+        public Message next() {
             var next = source.next();
-            @SuppressWarnings("unchecked")
-            var result = (M) next.toMessage();
+            var result = next.toMessage();
             return result;
         }
     }

server/src/main/kotlin/io/spine/server/event/Just.kt

@@ -38,7 +38,7 @@ import io.spine.server.tuple.Tuple
  *
  * @param E the type of the event.
  */
-public class Just<E : EventMessage>(event: E) : Tuple<E>(event) {
+public class Just<E : EventMessage>(event: E) : Tuple(event) {
 
     public companion object {