Value: add where() with Supplier<T> parameters

* Add `<T> Value.where(boolean, Supplier<T>, Supplier<T>)`
* Add `Optional<T> Value.where(boolean, Supplier<T>)`

CHANGELOG

@@ -4,6 +4,8 @@ CHANGELOG
 0.3.0
 -----
 
+* Add `<T> Value.where(boolean, Supplier<T>, Supplier<T>)`
+* Add `Optional<T> Value.where(boolean, Supplier<T>)`
 * Add `.travis-support`
 * Avoid danger of JVM-level deadlock during `Value` initialisation
 * Avoid danger of JVM-level deadlock during `Condition` initialisation

README.adoc

@@ -201,6 +201,16 @@ if (isTrue()) {
 String result = isTrue() ? TRUE : FALSE;
 ----
 
+[[source,java]]
+----
+final String result = Value.where(isTrue(), () -> TRUE, () -> FALSE);
+----
+
+[[source,java]]
+----
+final Optional<String> result = Value.where(isTrue(), () -> TRUE);
+----
+
 [[source,java]]
 ----
 final String result = Value.<String>where(isTrue()).then(() -> TRUE)

src/main/java/net/kemitix/conditional/Value.java

@@ -21,6 +21,7 @@
 
 package net.kemitix.conditional;
 
+import java.util.Optional;
 import java.util.function.Supplier;
 
 /**
@@ -55,6 +56,22 @@ public interface Value {
         return where(!clause);
     }
 
+    static <T> T where(
+            boolean clause,
+            Supplier<T> trueSupplier,
+            Supplier<T> falseSupplier
+                      ) {
+        return Value.<T>where(clause).then(trueSupplier)
+                                     .otherwise(falseSupplier);
+    }
+
+    static <T> Optional<T> where(
+            boolean clause,
+            Supplier<T> trueSupplier
+                                ) {
+        return Optional.ofNullable(Value.where(clause, trueSupplier, () -> null));
+    }
+
     /**
      * An intermediate state in determining the final {@link Value}.
      *

src/test/java/net/kemitix/conditional/ValueTest.java

@@ -3,6 +3,8 @@ package net.kemitix.conditional;
 import lombok.val;
 import org.junit.Test;
 
+import java.util.Optional;
+
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
@@ -15,7 +17,39 @@ public class ValueTest {
     private static final String FALSE = "false";
 
     @Test
-    public void valueWhereTrueIsTrue() {
+    public void valueWhereClauseIsTrueTypeSafe() {
+        //when
+        final String result = Value.where(true, () -> TRUE, () -> FALSE);
+        //then
+        assertThat(result).isEqualTo(TRUE);
+    }
+
+    @Test
+    public void valueWhereClauseIsFalseTypeSafe() {
+        //when
+        final String result = Value.where(false, () -> TRUE, () -> FALSE);
+        //then
+        assertThat(result).isEqualTo(FALSE);
+    }
+
+    @Test
+    public void valueWhereClauseIsTrueIsOptional() {
+        //when
+        final Optional<String> result = Value.where(true, () -> TRUE);
+        //then
+        assertThat(result).contains(TRUE);
+    }
+
+    @Test
+    public void valueWhereClauseIsFalseIsEmptyOptional() {
+        //when
+        final Optional<String> result = Value.where(false, () -> TRUE);
+        //then
+        assertThat(result).isEmpty();
+    }
+
+    @Test
+    public void valueWhereClauseIsTrue() {
         //when
         val result = Value.<String>where(true).then(() -> TRUE)
                                               .otherwise(() -> FALSE);
@@ -24,7 +58,7 @@ public class ValueTest {
     }
 
     @Test
-    public void valueWhereFalseIsFalse() {
+    public void valueWhereClauseIsFalse() {
         //when
         val result = Value.<String>where(false).then(() -> TRUE)
                                                .otherwise(() -> FALSE);