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New feature: .mapTo(U) and .mapToVoid() for Value<T> #3086

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Merged
merged 5 commits into from
Nov 7, 2025
Merged

New feature: .mapTo(U) and .mapToVoid() for Value<T> #3086

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a9c5c55
New feature: .as(U) and .voided() for Value<T>
adamkopec Nov 4, 2025
d0c911a
Merge branch 'main' into feature/as-and-voided
adamkopec Nov 6, 2025
1ce4c46
New feature: .mapTo(U) and .mapToVoid() for Value<T>
adamkopec Nov 7, 2025
9d3a3d1
Merge remote-tracking branch 'origin/feature/as-and-voided' into feat…
adamkopec Nov 7, 2025
333fc3f
New feature: .mapTo(U) and .mapToVoid() for Value<T>
adamkopec Nov 7, 2025
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8 changes: 8 additions & 0 deletions vavr/src/main/java/io/vavr/Value.java
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Expand Up @@ -416,6 +416,14 @@ default T getOrNull() {
return isEmpty() ? null : get();
}

default <U> Value<U> as(U val) {
return map((ignored) -> val);
}

default Value<Void> voided() {
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@pivovarit pivovarit Nov 6, 2025

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It's probably a bit too specific - with the other method, people can just write as(null) or with(null) and that's probably clearer than guessing what "voided" actually means

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@achinaou achinaou Nov 6, 2025

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There are two advantages to using an explicit method: it clarifies the intent (which is good for code-reviews), and it avoids depending on type inference of the whole expression for the Void type.

For example, in our company we use a dedicated, Function<Object, Void> replaceWithVoid(), for this case as opposed to the <T> Function<Object, T> replaceWith(Supplier<? extends T> value) that we also have.

So, maybe with better naming there is a place for such a method?

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@pivovarit pivovarit Nov 6, 2025

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This is a good point actually - you'd need to cast to Void to get the same semantics

Do you have an idea for a better name?

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@adamkopec adamkopec Nov 6, 2025

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just a comment about the name, guys - I tried to follow the naming I'm the most familiar with, which is the one from cats' FunctorOps helper. there is an as(X) and void() there. in Java we can't do void, cause it's a keyword, but I'm happy to change it to whatever you suggest :)

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@achinaou achinaou Nov 6, 2025 •
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I’m also most familiar with the Typelevel/ZIO terminology of as and void/unit!

However, since Vavr’s main inspiration is Scala’s standard library with the terminology adapted to Java, I think the same strategy could apply here as well.

For developers coming from the Typelevel/ZIO ecosystems, .as and .voided would feel most familiar. But from the Scala stdlib perspective, and Vavr’s existing API, the .as* prefix conventionally signals a wrapper type conversion (e.g., List#asJava()), so reusing it for content replacement could break established intuition.

So, I think the methods .with(T) and .withVoid() are good choices as they build on the idea of "wither" methods (that may also come natively to Java), but without referring to a specific field, suggesting replacement of the Value’s content.

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@achinaou achinaou Nov 7, 2025 •
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Another not bad choice I think is the mapTo(T) / mapToVoid() option which is easily discoverable and cognitively closer to how someone would think about what would happen given an established intuition for map.

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@pivovarit pivovarit Nov 7, 2025

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I think I like this option the most - as sounds like it's close to asJava() method family. Also, I think that alignment to Scala should have much lower priority than years ago.

@adamkopec what do you think about mapTo/mapToVoid ?

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@adamkopec adamkopec Nov 7, 2025

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it's actually a very good idea, I updated the PR. @achinaou - you proposed something that is both easy to understand and not controversial. thx!

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@achinaou achinaou Nov 8, 2025

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Really glad I could help!

return map((ignored) -> null);
}

/**
* Checks if this {@code Value} is asynchronously (short: async) computed.
* <p>
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5 changes: 5 additions & 0 deletions vavr/src/main/java/io/vavr/collection/TreeSet.java
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Expand Up @@ -1017,6 +1017,11 @@ public <U> SortedSet<U> zipWithIndex(BiFunction<? super T, ? super Integer, ? ex
return TreeSet.ofAll(Comparators.naturalComparator(), iterator().zipWithIndex(mapper));
}

@Override
public TreeSet<Void> voided() {
return map((o1, o2) -> 0, ignored -> null);
}

// -- Object

@Override
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19 changes: 19 additions & 0 deletions vavr/src/test/java/io/vavr/AbstractValueTest.java
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Expand Up @@ -218,6 +218,25 @@ public void shouldReturnValueWhenGetOrNullOfNonEmpty() {
assertThat(of(1).getOrNull()).isEqualTo(1);
}

// -- as
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@pivovarit pivovarit Nov 7, 2025

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those are outdated

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@adamkopec adamkopec Nov 7, 2025

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fixed 😅


@TestTemplate
public void shouldExecuteAsCorrectly() {
assertThat(empty().as(1)).isEqualTo(empty().as(2));
assertThat(of(2).as(1)).isEqualTo(of(3).as(1));
assertThat(of(2).as(1)).isEqualTo(of(3).map(ignored -> 1));
assertThat(of(3).as(2)).isEqualTo(of(1).map(ignored -> 2));
}

// -- voided
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@pivovarit pivovarit Nov 7, 2025

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and this

let's update it for now, but I will eventually get rid of these comments and replace with nested junit test classes wherever it makes sense

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@adamkopec adamkopec Nov 7, 2025

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updated both :)


@TestTemplate
public void shouldExecuteVoidedCorrectly() {
assertThat(empty().voided()).isEqualTo(empty());
assertThat(of(1).voided()).isEqualTo(of(1).as(null));
assertThat(of(1).voided()).isEqualTo(of(1).map(ignored -> null));
}

// -- forEach

@TestTemplate
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7 changes: 7 additions & 0 deletions vavr/src/test/java/io/vavr/collection/BitSetTest.java
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Expand Up @@ -565,6 +565,13 @@ public void shouldReturnTailOfNonEmptyHavingReversedOrder() {
// BitSet can't have reverse order
}

@Test
@Override
public void shouldExecuteVoidedCorrectly() {
assertThat(empty().voided()).isEqualTo(empty());
assertThat(of(1).voided()).isEqualTo(of((Integer)null));
}

// -- classes

private static final class Mapper<T> implements Serializable {
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7 changes: 7 additions & 0 deletions vavr/src/test/java/io/vavr/collection/TreeSetTest.java
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Expand Up @@ -411,4 +411,11 @@ public void shouldZipAllEmptyAndNonNil() {
@Disabled
public void shouldZipAllNonEmptyAndNil() {
}

@Test
@Override
public void shouldExecuteVoidedCorrectly() {
assertThat(empty().voided()).isEqualTo(empty());
assertThat(of(1).map(ignored -> null)).isEqualTo(of(1).voided());
}
}