Return Nullable instead of Optional<T>

[Kofituo]

Is there way to return a nullable value instead of a value wrapped in Optional<T>?
The difficulty is Optional<T> works with Andriod Api Version 24+ (but my projects starts from Api 21) and since the main language for andriod programming is Kotlin, it would be better to use Kotlin's way of handling nullable values i.e. using ? operator among others

A possible solution would be to rewrite the Optional class in Java (since Kotlin's companion objects are different from Java's static keyword), preserving the parts I'd use, but I feel using the Kotlin syntax integrates more with my project

[Dushistov]

There are drop-in-replacement for standard optional class, it can be activated like this:

 JavaConfig::new(output_dir, "com.company".into())
.use_optional_package("com.hadisatrio.optional".into())

and in app/build.gradle I have

dependencies {
  ...
    implementation 'com.github.dushistov:Optional:9016463'

In theory you can patch jni-include.rs like this:

foreign_typemap!(
    ($p:r_type) <T: SwigForeignClass> Option<T> => jlong {
        $out = match $p {
            Some(x) => {
                let ptr = <swig_subst_type!(T)>::box_object(x);
                debug_assert_ne!(0, ptr);
                ptr
            }
            None => 0,
        };
    };
    ($p:f_type) => "@Nullable swig_f_type!(T, NoNullAnnotations)" r#"
        $out;
        if ($p != 0) {
            $out = new swig_f_type!(T, NoNullAnnotations)(InternalPointerMarker.RAW_PTR, $p);
        } else {
            $out = null;
        }
"#;
);

[Kofituo]

Okay thanks I'll try it out

[Kofituo]

Can I just put the path in the java_glue.rs.in file?or it has to be the jni_include.rs file?

[Dushistov]

In theory you should be able to rewrite any standard rule that defined in jni-include.rs in your file.rs.in . But looks like rewriting generic rule contains some bug,
so I leave this issue open until I fixed the rewriting issue.

[Kofituo]

Okay sure

[Jonathas-Conceicao]

I've recently ran into the same problem, the drop-in-replacement solved the issue but I had to use

dependencies {
    implementation 'com.github.dushistov:Optional:develop-SNAPSHOT'
    ...
}

Due to the empty method that is only available on the develop branch.