Merge pull request #147 from bejibx/master

Add Optional#mapToBoolean(ToBooleanFunction) method

stream/src/main/java/com/annimon/stream/Optional.java

@@ -7,6 +7,8 @@
 import com.annimon.stream.function.ToDoubleFunction;
 import com.annimon.stream.function.ToIntFunction;
 import com.annimon.stream.function.ToLongFunction;
+import com.annimon.stream.function.ToBooleanFunction;
+
 import java.util.NoSuchElementException;
 
 /**
@@ -237,7 +239,21 @@ public OptionalDouble mapToDouble(ToDoubleFunction<? super T> mapper) {
         if (!isPresent()) return OptionalDouble.empty();
         return OptionalDouble.of(mapper.applyAsDouble(value));
     }
-
+
+    /**
+     * Invokes mapping function on inner value if present.
+     *
+     * @param mapper  mapping function
+     * @return an {@code OptionalBoolean} with transformed value if present,
+     *         otherwise an empty {@code OptionalBoolean}
+     * @throws NullPointerException if value is present and
+     *         {@code mapper} is {@code null}
+     */
+    public OptionalBoolean mapToBoolean(ToBooleanFunction<? super T> mapper) {
+        if (!isPresent()) return OptionalBoolean.empty();
+        return OptionalBoolean.of(mapper.applyAsBoolean(value));
+    }
+
     /**
      * Invokes mapping function with {@code Optional} result if value is present.
      * 

stream/src/main/java/com/annimon/stream/function/ToBooleanFunction.java

@@ -0,0 +1,18 @@
+package com.annimon.stream.function;
+
+/**
+ * Represents a function which produces an {@code boolean}-valued result from input argument.
+ *
+ * @param <T> the type of the input of the function
+ * @see Function
+ */
+public interface ToBooleanFunction<T> {
+
+    /**
+     * Applies this function to the given argument.
+     *
+     * @param t  an argument
+     * @return the function result
+     */
+    boolean applyAsBoolean(T t);
+}

stream/src/test/java/com/annimon/stream/OptionalTest.java

@@ -4,10 +4,12 @@
 import com.annimon.stream.function.Function;
 import com.annimon.stream.function.Predicate;
 import com.annimon.stream.function.Supplier;
+import com.annimon.stream.function.ToBooleanFunction;
 import com.annimon.stream.function.ToDoubleFunction;
 import com.annimon.stream.function.ToIntFunction;
 import com.annimon.stream.function.ToLongFunction;
 import com.annimon.stream.function.UnaryOperator;
+import com.annimon.stream.test.hamcrest.OptionalBooleanMatcher;
 import com.annimon.stream.test.hamcrest.OptionalDoubleMatcher;
 import com.annimon.stream.test.hamcrest.OptionalIntMatcher;
 import com.annimon.stream.test.hamcrest.OptionalLongMatcher;
@@ -309,6 +311,23 @@ public double applyAsDouble(String t) {
         assertThat(result, OptionalDoubleMatcher.hasValueThat(closeTo(0.65, 0.0001)));
     }
 
+    @Test
+    public void testMapToBoolean() {
+        final ToBooleanFunction<String> mapper = new ToBooleanFunction<String>() {
+            @Override
+            public boolean applyAsBoolean(String s) {
+                return "true".equalsIgnoreCase(s);
+            }
+        };
+
+        OptionalBoolean result;
+        result = Optional.<String>empty().mapToBoolean(mapper);
+        assertThat(result, OptionalBooleanMatcher.isEmpty());
+
+        result = Optional.of("true").mapToBoolean(mapper);
+        assertThat(result, OptionalBooleanMatcher.hasValueThat(is(true)));
+    }
+
     @Test
     public void testFlatMapAsciiToString() {
         Optional<String> result = Optional.of(65)