Top-level packageName

Language Design
1

Not wanting to resurrect a 6-year old topic I have a similar requirement but not just for logging. Has the ability to retrieve the packageName at the top-level in a file been added since then? I haven’t been able to find anything.

Given my more varied requirements the most succinct thing I could come up with was this (keeping it in the ‘logger’ vein for this example):

private val packageName: String = (object {}).javaClass.packageName
private val logger = LoggerFactory.getLogger(packageName)

This still feels somewhat contorted to get what should be a readily available attribute.

TIA.

2

I believe you could use inline functions here

inline fun packageName() = (object {}).javaClass.packageName

and then I think you can use it anywhere

3

This will create new object in the heap every time it is called. Not good for GC.

4

You have to do that though. The point of the inline function here is to create a new anonymous class where it’s called, so that the class has that package. What you can do is have a private val packageName = packageName() at the file level

5

That’s why I think we need special function in Kotlin JVM library, what will return synthetic class (like SomeFileKt.class) for top-level functions.

1 Like
6

Thanks @kyay10 for the inline fun. I was close on that but didn’t quite get there. And yes, I’d replace the existing code to set the val because the value is used in a lot of places so the object creation would need to be minimized.

Hopefully we’ll see a language/lib-provided mechanism in the (near?) future.

Thanks again.

1 Like
7

Another hack:

inline fun packageName(noinline block: () -> Unit): String = block.javaClass.packageName

val pkg = packageName{}

It doesn’t allocate anything per use and should be generally quick enough to be used directly in the code, but a huge drawback is its non-standard calling style. Implementation can’t be easily replaced in the future if needed. Also, it creates a separate class and its instance per each call-site.

8

Are you sure that this doesn’t create instance block every time it’s called?

9

Kotlin compiler is smart enough to recognize if it needs a closure or just a static function and in the latter case it uses a singleton:

fun test1() {
    println(packageName{})
}

fun test2(x: String) {
    println(packageName{ x })
}

  public static final void test1();
    Code:
       0: getstatic     #23                 // Field Test1Kt$test1$1.INSTANCE:LTest1Kt$test1$1;
       3: checkcast     #25                 // class kotlin/jvm/functions/Function0
       6: astore_0
       7: iconst_0
       8: istore_1
       9: aload_0
      10: invokevirtual #29                 // Method java/lang/Object.getClass:()Ljava/lang/Class;
      13: invokevirtual #34                 // Method java/lang/Class.getPackageName:()Ljava/lang/String;
      16: dup
      17: ldc           #36                 // String getPackageName(...)
      19: invokestatic  #42                 // Method kotlin/jvm/internal/Intrinsics.checkNotNullExpressionValue:(Ljava/lang/Object;Ljava/lang/String;)V
      22: astore_0
      ...

  public static final void test2(java.lang.String);
    Code:
       0: aload_0
       1: ldc           #62                 // String x
       3: invokestatic  #65                 // Method kotlin/jvm/internal/Intrinsics.checkNotNullParameter:(Ljava/lang/Object;Ljava/lang/String;)V
       6: new           #67                 // class Test1Kt$test2$1
       9: dup
      10: aload_0
      11: invokespecial #70                 // Method Test1Kt$test2$1."<init>":(Ljava/lang/String;)V
      14: checkcast     #25                 // class kotlin/jvm/functions/Function0
      17: astore_1
      18: iconst_0
      19: istore_2
      20: aload_1
      21: invokevirtual #29                 // Method java/lang/Object.getClass:()Ljava/lang/Class;
      24: invokevirtual #34                 // Method java/lang/Class.getPackageName:()Ljava/lang/String;
      27: dup
      28: ldc           #36                 // String getPackageName(...)
      30: invokestatic  #42                 // Method kotlin/jvm/internal/Intrinsics.checkNotNullExpressionValue:(Ljava/lang/Object;Ljava/lang/String;)V
      33: astore_1
      ...
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