question folks: if I need to define a KN function that will be called on Objective-C that returns a ...

# kotlin-native

[ivan.savytskyi]

question folks: if I need to define a KN function that will be called on Objective-C that returns a string and it has this signature override fun foo(): CPointer<ByteVar>?, should I use StableRef like:

override fun foo(): CPointer<ByteVar>? {
        return StableRef
            .create(name.encodeToByteArray())
            .asCPointer()
            .rawValue
            .let { interpretCPointer(it) }
    }

[Dominaezzz]

⚠️ No! ⚠️

[Dominaezzz]

Or rather, I don't think that does what you think it does.

[Dominaezzz]

If you want to return a CPointer<ByteVar>, you're gonna have to allocate memory and return it.

[Dominaezzz]

How long do you need this string for? What's the scope of it?

[Dominaezzz]

Do you basically just want to malloc?

[Dominaezzz]

You can also just do this and let the caller decide.

override fun foo(): CValues<ByteVar>? {
    return name.encodeToByteArray().cstr
}

[olonho]

@ivan.savytskyi why do you need that? why not return Kotlin's string and rely upon interop conversions?

[ivan.savytskyi]

The issues that this function is defined by the Objective-C protocol, I would love to return just string but c interop tool generated this signature @kotlinx.cinterop.ObjCMethod public abstract fun foo(): kotlinx.cinterop.CPointer<kotlinx.cinterop.ByteVar

[ivan.savytskyi]

The issue is that I don't really know what is the scope of this string should be, as this function is supposed to be called sometime later by external C library, that I don't have control

[ivan.savytskyi]

this is the declaration in the header file:

@protocol XXX <NSObject>
....
@property (nonatomic, readonly) const char *foo;`

[ivan.savytskyi]

I was thinking of return name.cstr.getPointer(Arena()) but I'm not sure if this is correct usage as well

[Dominaezzz]

All you need to decide is when/where you want to free the allocated memory.