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Propose Try.toEither(Throwable => L) #2724

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Propose Try.toEither(Throwable => L) #2724

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a6db1e1
Try::toEither with throwable mapper
eslep Oct 28, 2022
839cc8a
Code review improvements
eslep Oct 31, 2022
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15 changes: 15 additions & 0 deletions src/main/java/io/vavr/control/Try.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1132,6 +1132,21 @@ public final Either<Throwable, T> toEither() {
}
}

/**
* Converts this {@code Try} to an {@link Either}, converting the Throwable (if present)
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I'm proposing this change for the documentation so that it is more precise in meaning, because one could legitimately use a Try value to wrap a Throwable instance as a success value.

Suggested change
* Converts this {@code Try} to an {@link Either}, converting the Throwable (if present)
* Converts this {@code Try} to an {@link Either}, converting the Throwable (in the failure case)

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I had the same impression that the wording was strange, but I kept this to stay consistent with toValidation(Throwable => U).

I would make this doc change to both of these methods then, since your point applies to both cases.

* to a left value using the passed {@link Function}
*
* @param throwableMapper A transformation from throwable to the left type of the new {@code Either}
* @return A new {@code Either}
*/
public final <L> Either<L, T> toEither(Function<? super Throwable, ? extends L> throwableMapper) {
if (isFailure()) {
return Either.left(throwableMapper.apply(getCause()));
} else {
return Either.right(get());
}
}

/**
* Converts this {@code Try} to a {@link Validation}.
*
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9 changes: 9 additions & 0 deletions src/test/java/io/vavr/control/TryTest.java
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Expand Up @@ -969,6 +969,15 @@ public void shouldConvertFailureToEitherLeftSupplier() {
assertThat(failure().toEither(() -> "test").isLeft()).isTrue();
}

@Test
public void shouldConvertFailureToEitherLeftMapper() {
final Try<Object> failure = Try.failure(new RuntimeException("a certain value"));
final Either<Boolean, Object> either = failure.toEither(t ->
t.getMessage().equals("a certain value")
);
assertThat(either).isEqualTo(Either.left(true));
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@nfekete nfekete Oct 31, 2022 •
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I'd probably replace the test code in a way that limits the number of comparisons to one, which would be the one in the assertion itself.
You could use a mapper function that extracts the message from the exception and use that as the left value to compare to in the assertion. This would make the code both shorter, and — in my opinion — easier to understand, since it would have a slightly less degree of indirection.

Suggested change
final Either<Boolean, Object> either = failure.toEither(t ->
t.getMessage().equals("a certain value")
);
assertThat(either).isEqualTo(Either.left(true));
final Either<Boolean, Object> either = failure.toEither(Throwable::getMessage);
assertThat(either).isEqualTo(Either.left("a certain value"));

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Sure, sounds much better that way 👍 I also felt a bit weird using Throwable => Boolean as my function where many people would maybe expect that to then be Predicate<Throwable>. I can see also how the equals looks like an assertion.

Main point was just to have a clear expected value returned by the function, so the suggestion sounds great

}


// -- toValidation

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