How to express array annotation argument in Kotlin?

Question

When annotation has an array argument with basic type like String or Int it is straightforward how to use that:

public @interface MyAnnotation{
  String[] props();
}

@MyAnnotation(props = ["A", "B", "C"])
class Foo {}

Unfortunately that does not work for values that are annotations themselves.

An example is org.springframework.context.annotation.PropertySources:

public @interface PropertySources {
  PropertySource[] value();
}

public @interface PropertySource { 
  String[] value();
}

In Java syntax usage is

@PropertySources({
    @PropertySource({"A", "B", "C"}),
    @PropertySource({"D", "E", "F"}),
})
class Foo{}

But in Kotlin the code with similar approach does not compile

@PropertySources([
    @PropertySource(["A", "B", "C"]),
    @PropertySource(["D", "E", "F"]),
])
class Foo{}

How to express this annotation array nesting construction in Kotlin?

Tom · Accepted Answer · 2021-12-30 12:50:37Z

5

Add value = and remove the @ from the child annotation declaration:

@PropertySources(value = [
  PropertySource("a", "b"),
  PropertySource("d", "e"),
])
class Foo

Also note that @PropertySource is @Repeatable so you can do:

@PropertySource("a", "b")
@PropertySource("d", "e")
class Foo

answered Dec 30, 2021 at 12:50

Tom

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2 Comments

The trick is in the "value =". Ok, great. Are you sure the second code block compiles?

Yes, note i used latest kotlin (1.6.10)