Mastering Kotlin

Default targets

If a use-site is not specified for an added annotation, the target will be chosen based on the targets specified on the annotation.

Let's look at the following custom annotation:

@Target(AnnotationTarget.PROPERTY_GETTER)annotation class ColorRes

This annotation can be applied to property getters, but not other targets. Therefore, in this example, the code will not compile:

class ViewModel( @ColorRes val resId:Int ) . // will not compile

However, if we specify the get use-site, then the code will compile just fine:

class ViewModel( @get:ColorRes val resId:Int )

If an annotation declaration doesn't include the @Target annotation, the following targets will be applicable:

• class
• property
• field
• local_variable
• value_parameter