fix(solve-handler): Change .cast(..) onError param to BiFunction (#240)

src/main/java/io/github/joselion/maybe/SolveHandler.java

@@ -3,6 +3,7 @@
 import static java.util.Objects.isNull;
 
 import java.util.Optional;
+import java.util.function.BiFunction;
 import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Predicate;
@@ -458,23 +459,27 @@ public <U> SolveHandler<U, ClassCastException> cast(final Class<U> type) {
   /**
    * If the value is present, casts the value to the provided {@code type}
    * class. If the value is not assignable to {@code type}, maps the error with
-   * the provided {@code onError} function, which receives the produced
-   * {@link ClassCastException} as input. If the error is present, returns a
-   * handler with the same error so it can be propagated downstream.
+   * the provided {@code onError} bi-function, which receives the value and the
+   * produced {@link ClassCastException} as inputs. If the error is present,
+   * returns a handler with the same error so it can be propagated downstream.
    *
    * @param <U> the type of the cast value
    * @param <X> the type of the mapped exception
    * @param type the class instance of the type to cast
-   * @param onError a function to map the error in case of failure
+   * @param onError a bi-function to map the error in case of failure
    * @return a handler with either the cast value or the mapped error
    */
   public <U, X extends Throwable> SolveHandler<U, X> cast(
     final Class<U> type,
-    final Function<ClassCastException, ? extends X> onError
+    final BiFunction<? super T, ClassCastException, ? extends X> onError
   ) {
-    return this
-      .solve(type::cast)
-      .mapError(ClassCastException.class, onError);
+    return this.solve(prev -> {
+      try {
+        return type.cast(prev);
+      } catch (ClassCastException e) {
+        throw onError.apply(prev, e);
+      }
+    });
   }
 
   /**

src/test/java/io/github/joselion/maybe/SolveHandlerTest.java

@@ -6,6 +6,8 @@
 import static org.assertj.core.api.InstanceOfAssertFactories.THROWABLE;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.ArgumentMatchers.isA;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 
@@ -649,7 +651,7 @@
       @Nested class and_the_value_is_an_instance_of_the_type {
         @Test void returns_a_handler_with_the_cast_value() {
           final var anyValue = (Object) "Hello";
-          final var mapperSpy = Spy.function((ClassCastException e) -> new RuntimeException(e));
+          final var mapperSpy = Spy.biFunction((Object x, ClassCastException e) -> new RuntimeException(e));
           final var handler = SolveHandler.from(anyValue);
           final var overloads = List.of(
             handler.cast(String.class),
@@ -661,7 +663,7 @@
             assertThat(overload.error()).isEmpty();
           });
 
-          verify(mapperSpy, never()).apply(any());
+          verify(mapperSpy, never()).apply(any(), any());
         }
       }
 
@@ -680,21 +682,21 @@
 
         @Nested class and_the_error_mapper_is_provided {
           @Test void returns_a_handler_with_the_mapped_error() {
-            final var mapperSpy = Spy.function((ClassCastException e) -> FAILURE);
+            final var mapperSpy = Spy.biFunction((Integer x, ClassCastException e) -> FAILURE);
             final var handler = SolveHandler.from(3).cast(String.class, mapperSpy);
 
             assertThat(handler.success()).isEmpty();
             assertThat(handler.error()).contains(FAILURE);
 
-            verify(mapperSpy).apply(any(ClassCastException.class));
+            verify(mapperSpy).apply(eq(3), isA(ClassCastException.class));
           }
         }
       }
     }
 
     @Nested class when_the_error_is_present {
       @Test void returns_a_handler_with_the_error() {
-        final var mapperSpy = Spy.function((ClassCastException e) -> new RuntimeException(e));
+        final var mapperSpy = Spy.biFunction((Object x, ClassCastException e) -> new RuntimeException(e));
         final var handler = SolveHandler.failure(FAILURE);
         final var overloads = List.of(
           handler.cast(String.class),
@@ -706,7 +708,7 @@
           assertThat(overload.error()).get().isSameAs(FAILURE);
         });
 
-        verify(mapperSpy, never()).apply(any());
+        verify(mapperSpy, never()).apply(any(), any());
       }
     }
   }

src/test/java/io/github/joselion/testing/Spy.java

@@ -3,6 +3,7 @@
 import static org.mockito.AdditionalAnswers.delegatesTo;
 import static org.mockito.Mockito.mock;
 
+import java.util.function.BiFunction;
 import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Supplier;
@@ -37,14 +38,27 @@ public static <T> T lambda(final T lambda) {
    * Creates a spy of a generic {@link Function} interface.
    *
    * @param <T> the type of the input to the function
-   * @param <U> the type of the result of the function
+   * @param <R> the type of the result of the function
    * @param function the function to spy on
    * @return a spy of the provided function
    */
-  public static <T, U> Function<T, U> function(final Function<T, U> function) {
+  public static <T, R> Function<T, R> function(final Function<T, R> function) {
     return lambda(function);
   }
 
+  /**
+   * Creates a spy of a generic {@link BiFunction} interface.
+   *
+   * @param <T> the type of the first input to the function
+   * @param <U> the type of the second input to the function
+   * @param <R> the type of the result of the function
+   * @param biFunction the bi-function to spy on
+   * @return a spy of the provided function
+   */
+  public static <T, U, R> BiFunction<T, U, R> biFunction(final BiFunction<T, U, R> biFunction) {
+    return lambda(biFunction);
+  }
+
   /**
    * Creates a spy of a generic {@link Consumer} interface.
    *