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NonNull and java.lang.Optional orElse() [message #1749868]

Tue, 13 December 2016 06:36

Eclipse User

Hi

To just accept a null in case a Option is empty, you can use

Optional<String> opt = ....;
@NonNull str1 = "str1";
@Nullable str2 = read();

@Nullable String res0 = opt.orElse(null);
@NonNull String res1 = opt.orElse(str1);
@Nullable String res2 = opt.orElse(str2);

Is there a way to make this work?
Or would it be needed to ask for a new method in Optional, e.g. orElseNullable(), orNull() ?

Frank

Re: NonNull and java.lang.Optional orElse() [message #1749877 is a reply to message #1749868]

Tue, 13 December 2016 08:42

Eclipse User

In class Checks we provide a solution for the first variant:

public static <T> @Nullable T asNullable(@NonNull Optional<T> optional)

Providing a nullable fallback is not supported. Is that really a useful pattern? What's the use of the fallback when it cannot be relied upon itself?

Stephan

Re: NonNull and java.lang.Optional orElse() [message #1750180 is a reply to message #1749877]

Fri, 16 December 2016 14:53

Eclipse User

Hi Stephan,

If there would be a way to say "the return nullability is the same as the one of the first parameter", this would solve it perfectly.

But as i understand, with Check.asNullable, I can annotation
@NonNull T Optional.orElse( @NonNull T t )
and replace those places where I used orElse(null) with the Check.asNullable.

thanks
Frank

Re: NonNull and java.lang.Optional orElse() [message #1750219 is a reply to message #1750180]

Sun, 18 December 2016 17:12

Eclipse User

do you envision s.t. like

<T> T fromOptionalOrElse(@NonNull Optional<@NonNull T> optional, T fallback)

Here <T> could be either a nullable or a nonnull type - to be inferred from fallback and the target type, whereas the optional would use the nonnull variant of this type.

Still I don't understand whether/why you want a nullable fallback.

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