Hello there, I have a question regarding annotations. What is the difference between ```object Test...

# getting-started

[andylamax]

Hello there, I have a question regarding annotations.

What is the difference between

object Test {
  @get:Composable
  val primary: Color get() = TODO()
}

and

object Test {
  val primary: Color
  @Composeable
  get() = TODO()
}

Compose seem to be happy with the later and not with former. I though these where same. Anyone?

[knthmn]

In the latter the annotation is applied on the getter function. If you check @Composable, it is only applicable on

AnnotationTarget.FUNCTION, AnnotationTarget.TYPE, AnnotationTarget.TYPE_PARAMETER, AnnotationTarget.PROPERTY_GETTER

[andylamax]

and where is it being applied in the former?? I assume the getter as well, No?

[knthmn]

It is applied to the property or the backing field. You can try with the following

@Target(AnnotationTarget.FIELD)
annotation class FieldAnnotation
@Target(AnnotationTarget.PROPERTY_GETTER)
annotation class GetterAnnotation
@Target(AnnotationTarget.PROPERTY)
annotation class PropertyAnnotation

class Test {
    @FieldAnnotation val x1 = 0
    val x2 @FieldAnnotation get() = 0  // compilation error

    @GetterAnnotation val x3 = 0  // compilation error
    val x4 @GetterAnnotation get() = 0

    @PropertyAnnotation val x5 = 0
    val x6 @PropertyAnnotation get() = 0  // compilation error
}

[knthmn]

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.annotation/-annotation-target/

[andylamax]

I think you are confusing

object Test {
  @get:Composable  // Has @get:
  val primary: Color get() = TODO()
}

with

object Test {
  @Composable // No @get:
  val primary: Color get() = TODO()
}

The later indeed applies to the backing field. What does the former do?

[andylamax]

In other words, would this cause a compilation error? if so, why?

@Target(AnnotationTarget.FIELD)
annotation class FieldAnnotation
@Target(AnnotationTarget.PROPERTY_GETTER)
annotation class GetterAnnotation
@Target(AnnotationTarget.PROPERTY)
annotation class PropertyAnnotation

class Test {
    @get:GetterAnnotation val x3 = 0  // Getter annotation, applied on field with a 'get' directive
    val x4 get() = 0
}

[knthmn]

Sorry I misread the original post and answered the wrong question. I will leave this for someone who knows more.

[andylamax]

No worries mate. I do appreciate the effort

[Rein T]

@get: annotates a java getter.
can it be that Compose scans kotlin code?

[andylamax]

if @get: annotates the java getter, what does

val p @Annotation get() = ...

annotate??

[Rein T]

I agree that the normal behavior is exactly as you are stating it.
I verified with moving @get:Size to a get() in one of my project and it works just as good.

What I was thinking is that your problem is linked to how Composable scans the kotlin code and not applicable to @AnyAnnotation

[andylamax]

Then it is more of a Compose scan rather than an Annotations issue, right??

[Rein T]

that was my guessing..