runtime-compute: Change the way compose works with ToBoolean

runtime-parent/runtime-compute/src/main/java/com/speedment/runtime/compute/ToBoolean.java

@@ -125,10 +125,42 @@ default int compare(T first, T second) {
         return Boolean.compare(f, s);
     }
 
+    /**
+     * {@inheritDoc}
+     * <p>
+     * {@code ToBoolean} is a bit special when it comes to the
+     * {@code compose()}-method. If the {@code before} method returns
+     * {@code null}, the composed expression will return {@code false}. This is
+     * to remain compatible with how Speedment handles predicates in streams.
+     * To get a {@code ToBooleanNullable} that acts as you might expect, instead
+     * use {@link #compose}
+     *
+     * @param before the function to apply before this function is applied
+     * @param <V>  the input type of the {@code before} function
+     * @return  the composed expression
+     */
     @Override
-    default <V> ToBooleanNullable<V> compose(Function<? super V, ? extends T> before) {
+    default <V> ToBoolean<V> compose(Function<? super V, ? extends T> before) {
         @SuppressWarnings("unchecked")
         final Function<V, T> casted = (Function<V, T>) before;
         return ComposedUtil.composeToBoolean(casted, this);
     }
+
+    /**
+     * Returns a composed expression that first applies the {@code before}
+     * function to its input, and then applies this function to the result.
+     * If evaluation of either function throws an exception, it is relayed to
+     * the caller of the composed function.
+     *
+     * @param before the function to apply before this function is applied
+     * @param <V>  the input type of the {@code before} function
+     * @return  the composed expression
+     *
+     * @since 3.1.2
+     */
+    default <V> ToBooleanNullable<V> composeNullable(Function<? super V, ? extends T> before) {
+        @SuppressWarnings("unchecked")
+        final Function<V, T> casted = (Function<V, T>) before;
+        return ComposedUtil.composeToBooleanAsNullable(casted, this);
+    }
 }

runtime-parent/runtime-compute/src/main/java/com/speedment/runtime/compute/internal/expression/ComposedUtil.java

@@ -455,10 +455,24 @@ public Double apply(T object) {
      * @param <A>  the type returned by {@code first}
      * @return  the composed expression
      */
-    public static <T, A> ToBooleanNullable<T> composeToBoolean(Function<T, A> before, ToBoolean<A> after) {
+    public static <T, A> ToBoolean<T> composeToBoolean(Function<T, A> before, ToBoolean<A> after) {
         return new ComposeToBoolean<>(before, after);
     }
 
+    /**
+     * Returns a new expression that first applies the {@code first} function
+     * and then passes the result to the {@code second} expression.
+     *
+     * @param before the first function to apply
+     * @param after  the expression to apply to the result
+     * @param <T>  the type of the initial input
+     * @param <A>  the type returned by {@code first}
+     * @return  the composed expression
+     */
+    public static <T, A> ToBooleanNullable<T> composeToBooleanAsNullable(Function<T, A> before, ToBoolean<A> after) {
+        return new ComposeToBooleanNullable<>(before, after);
+    }
+
     /**
      * Returns a new expression that first applies the {@code first} function
      * and then passes the result to the {@code second} expression.
@@ -470,18 +484,22 @@ public static <T, A> ToBooleanNullable<T> composeToBoolean(Function<T, A> before
      * @return  the composed expression
      */
     public static <T, A> ToBooleanNullable<T> composeToBooleanNullable(Function<T, A> before, ToBooleanNullable<A> after) {
-        return new ComposeToBoolean<>(before, after);
+        return new ComposeToBooleanNullable<>(before, after);
     }
 
     /**
-     * Internal implementation of the {@link ComposedExpression}.
+     * Internal implementation of the {@link ComposedExpression}. Booleans are
+     * handled a bit differently when it comes to {@code null}-values. If the
+     * {@code before}-function returns {@code null}, then the expression will
+     * always evaluate to {@code false}. This is to stay compatible with how
+     * Speedment handles predicates in streams.
      *
      * @param <T>      the outer input type
      * @param <A>      the inner input type
      * @param <AFTER>  the expression type of the {@code after} operation
      */
     private final static class ComposeToBoolean<T, A, AFTER extends ToBooleanFunction<A> & Expression<A>>
-        implements ComposedExpression<T, A>, ToBooleanNullable<T> {
+        implements ComposedExpression<T, A>, ToBoolean<T> {
 
         private final Function<T, A> before;
         private final AFTER after;
@@ -501,6 +519,41 @@ public AFTER secondStep() {
             return after;
         }
 
+        @Override
+        public boolean applyAsBoolean(T object) throws NullPointerException {
+            final A intermediate = before.apply(object);
+            return intermediate != null && after.applyAsBoolean(intermediate);
+        }
+    }
+
+    /**
+     * Internal implementation of the {@link ComposedExpression}.
+     *
+     * @param <T>      the outer input type
+     * @param <A>      the inner input type
+     * @param <AFTER>  the expression type of the {@code after} operation
+     */
+    private final static class ComposeToBooleanNullable<T, A, AFTER extends ToBooleanFunction<A> & Expression<A>>
+        implements ComposedExpression<T, A>, ToBooleanNullable<T> {
+
+        private final Function<T, A> before;
+        private final AFTER after;
+
+        ComposeToBooleanNullable(Function<T, A> before, AFTER after) {
+            this.before = requireNonNull(before);
+            this.after  = requireNonNull(after);
+        }
+
+        @Override
+        public Function<T, A> firstStep() {
+            return before;
+        }
+
+        @Override
+        public AFTER secondStep() {
+            return after;
+        }
+
         @Override
         public boolean applyAsBoolean(T object) throws NullPointerException {
             final A intermediate = before.apply(object);