How to rename a property's backing field in Kotlin

Question

EDIT (again): If anyone is interested, you can follow this issue on the tracker.

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EDIT: I know about backing properties and that they will cover most use cases. I'm not looking for a work around, I'm specifically looking if there is a way to name the backing field.

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You can easily rename the getter and setter of a property like so

@get:JvmName("getFancy")
@set:JvmName("setFancy")
var fancyProperty = ...

But I can't figure out how to change the name of a backing field, even using the @field target.

@field:JvmName("fancy")
var fancyProperty = ...

The above give an error:

This annotation is not applicable to target 'member property with backing field' and use site target '@field'

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Ultimately what I'm going for is interop with JavaFX. When defining a JavaFX property, you usually follow the following standard (with some additional code to make it lazy):

private ObjectProperty<Color> color = new SimpleObjectProperty<>(this, "color", DEFAULT_COLOR);

public ObjectProperty<Color> colorProperty() {
    return color;
}

public Color getColor() {
    return colorProperty.get();
}

public void setColor(Color color) {
    colorProperty().set(color);
}

So what I'm going for is something like this (though the @field obviously doesn't work):

@field:JvmName("color")
@get:JvmName("colorProperty")
val colorProperty: ObjectProperty<Color> =
    SimpleObjectProperty(this, "color", DEFAULT_COLOR)

var color
    get() = colorProperty.get()
    set(value) = colorProperty.set(value)

This would allow the binding capabilities of FXML (which use reflection), follow the standard conventions in Java, and still be nice and easy to use from Kotlin.

In this case I can't use a backing property because I need the color field to be a ObjectProperty<Color>, but the getter and setter for color should be a Color.

Luckily, the reflection from JavaFX is smart enough to still work with just the @get:JvmName("colorProperty"), but there are similar situations with overlapping field names that could use this renaming.

Answer 1

No it is not possible. The reason is, that there are cases where there is no backing field (and thus this property abstraction).

From the kotlin examples (creates no backing field):

val isEmpty: Boolean
    get() = this.size == 0

Hence the need for the backing properties workaround.