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New feature: Either.cond
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‎vavr/src/main/java/io/vavr/control/Either.java

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@@ -111,6 +111,101 @@ static <L, R> Either<L, R> narrow(Either<? extends L, ? extends R> either) {
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return (Either<L, R>) either;
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}
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/**
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* Decides which {@code Either<L, R>} to return, depending on the test value -
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* if it's true, the result will be a {@link Either.Right},
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* if it's false - the result will be a {@link Either.Left}
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*
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* @param test A {@code Boolean} value to evaluate
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* @param right A {@code Supplier<? extends R>} supplier of right value, called if test is true
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* @param left A {@code Supplier<? extends L>} supplier of left value, called if test is false
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* @param <L> Type of left value
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* @param <R> Type of right value
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*
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* @return {@code Either<L, R>} with right or left value, depending on the test condition evaluation
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*
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* @throws NullPointerException if any of the arguments is null
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* @author Adam Kopeć
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*/
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static <L, R> Either<L, R> cond(Boolean test, Supplier<? extends R> right, Supplier<? extends L> left) {
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Objects.requireNonNull(test, "test is null");
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Objects.requireNonNull(right, "right is null");
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Objects.requireNonNull(left, "left is null");
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return test ? right(right.get()) : left(left.get());
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}
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/**
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* Decides which {@code Either<L, R>} to return, depending on the test value -
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* if it's true, the result will be a {@link Either.Right},
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* if it's false - the result will be a {@link Either.Left}
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*
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* @param test A {@code Boolean} value to evaluate
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* @param right A n{@code R} right value, returned if test is true
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* @param left A {@code L} left value, returned if test is false
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* @param <L> Type of left value
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* @param <R> Type of right value
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*
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* @return {@code Either<L, R>} with right or left value, depending on the test condition evaluation
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*
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* @throws NullPointerException if any of the arguments is null
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* @author Adam Kopeć
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*/
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static <L, R> Either<L, R> cond(Boolean test, R right, L left) {
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Objects.requireNonNull(test, "test is null");
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Objects.requireNonNull(right, "right is null");
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Objects.requireNonNull(left, "left is null");
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return cond(test, () -> right, () -> left);
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}
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/**
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* Decides which {@code Either<L, R>} to return, depending on the test value -
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* if it's true, the result will be a {@link Either.Right},
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* if it's false - the result will be a {@link Either.Left}
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*
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* @param test A {@code Boolean} value to evaluate
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* @param right A {@code Supplier<? extends R>} supplier of right value, called if test is true
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* @param left A {@code L} left value, returned if test is false
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* @param <L> Type of left value
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* @param <R> Type of right value
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*
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* @return {@code Either<L, R>} with right or left value, depending on the test condition evaluation
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*
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* @throws NullPointerException if any of the arguments is null
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* @author Adam Kopeć
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*/
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static <L, R> Either<L, R> cond(Boolean test, Supplier<? extends R> right, L left) {
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Objects.requireNonNull(test, "test is null");
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Objects.requireNonNull(right, "right is null");
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Objects.requireNonNull(left, "left is null");
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return cond(test, right, () -> left);
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}
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/**
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* Decides which {@code Either<L, R>} to return, depending on the test value -
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* if it's true, the result will be a {@link Either.Right},
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* if it's false - the result will be a {@link Either.Left}
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*
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* @param test A {@code Boolean} value to evaluate
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* @param right A {@code R} right value, returned if test is true
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* @param left A {@code Supplier<? extends L>} supplier of left value, called if test is false
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* @param <L> Type of left value
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* @param <R> Type of right value
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*
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* @return {@code Either<L, R>} with right or left value, depending on the test condition evaluation
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*
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* @throws NullPointerException if any of the arguments is null
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* @author Adam Kopeć
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*/
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static <L, R> Either<L, R> cond(Boolean test, R right, Supplier<? extends L> left) {
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Objects.requireNonNull(test, "test is null");
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Objects.requireNonNull(right, "right is null");
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Objects.requireNonNull(left, "left is null");
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return cond(test, () -> right, left);
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}
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/**
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* Returns the left value.
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*

‎vavr/src/test/java/io/vavr/control/EitherTest.java

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Original file line numberDiff line numberDiff line change
@@ -32,6 +32,7 @@
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import static io.vavr.API.Right;
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import static org.assertj.core.api.Assertions.assertThatThrownBy;
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import static org.junit.jupiter.api.Assertions.assertThrows;
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import static org.junit.jupiter.api.Assertions.fail;
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@SuppressWarnings("deprecation")
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public class EitherTest extends AbstractValueTest {
@@ -333,6 +334,93 @@ public void shouldNarrowLeftEither() {
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}
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}
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@Nested
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public class CondTests {
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@Test
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public void shouldReturnRightIfTestTrue() {
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Either<String, Integer> either = Either.cond(true, () -> 21, () -> "vavr");
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assertThat(either).isEqualTo(Either.right(21));
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}
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@Test
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public void shouldReturnLeftIfTestFalse() {
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Either<String, Integer> either = Either.cond(false, () -> 21, () -> "vavr");
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assertThat(either).isEqualTo(Either.left("vavr"));
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}
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@Test
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public void shouldNotEvaluateRightSupplierOnFalse() {
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Either<String, Integer> either = Either.cond(false, () -> {
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fail("Should not be called");
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return 21;
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}, () -> "vavr");
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assertThat(either).isEqualTo(Either.left("vavr"));
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}
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@Test
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public void shouldNotEvaluateLeftSupplierOnTrue() {
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Either<String, Integer> either = Either.cond(true, () -> 21, () -> {
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fail("Should not be called");
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return "vavr";
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});
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assertThat(either).isEqualTo(Either.right(21));
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}
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private class Animal {
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String name;
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Animal(String name) { this.name = name; }
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@Override
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public boolean equals(Object o) {
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if (this == o) return true;
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if (!(o instanceof Animal)) return false;
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Animal other = (Animal) o;
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return name.equals(other.name);
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}
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@Override
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public int hashCode() {
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return name.hashCode();
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}
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}
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private class Dog extends Animal {
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Dog(String name) { super(name); }
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}
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private class Cat extends Animal {
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Cat(String name) { super(name); }
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}
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@Test
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public void shouldBeFineWithCovariantLeft() {
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Either<Animal, Integer> either = Either.cond(false, () -> 21, () -> new Cat("vavr"));
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assertThat(either).isEqualTo(Either.left(new Cat("vavr")));
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}
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@Test
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public void shouldBeFineWithCovariantRight() {
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Either<String, Animal> either = Either.cond(true, () -> new Dog("vavr"), () -> "vavr");
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assertThat(either).isEqualTo(Either.right(new Dog("vavr")));
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}
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@Test
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public void shouldMakeTheSameDecisionNoMatterHowItsCalled() {
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Either<String, Integer> e1 = Either.cond(true, () -> 21, () -> "vavr");
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Either<String, Integer> e3 = Either.cond(true, 21, "vavr");
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Either<String, Integer> e2 = Either.cond(true, 21, () -> "vavr");
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Either<String, Integer> e4 = Either.cond(true, () -> 21, "vavr");
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Either<String, Integer> e5 = Either.cond(false, () -> 21, () -> "vavr");
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Either<String, Integer> e6 = Either.cond(false, 21, "vavr");
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Either<String, Integer> e7 = Either.cond(false, 21, () -> "vavr");
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Either<String, Integer> e8 = Either.cond(false, () -> 21, "vavr");
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assertThat(List.of(e1, e2, e3, e4)).allMatch(e -> e.equals(Either.right(21)));
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assertThat(List.of(e5, e6, e7, e8)).allMatch(e -> e.equals(Either.left("vavr")));
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}
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}
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@Nested
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public class OrElseTests {
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