Difference between the behavior of const and @JvmField

[ythy]

1. const it only works with primitives and Strings:

class Constants {
  companion object {
    // won't compile
    const val FOO = Foo()
  }
}

2. accesses to a const val get inlined by the compiler, while @JvmFields don't

class Constants {
  companion object {
    @JvmField val FOO = Foo()
  }
}

Let's take the following code:

fun main(args: Array<String>) {
  println(Constants.FOO)
}

Here's what we get with @JvmField val FOO = Foo():

public final class MainKt {
   public static final void main(@NotNull String[] args) {
      Intrinsics.checkParameterIsNotNull(args, "args");
      Foo var1 = Constants.FOO;
      System.out.println(var1);
   }
}

And with const val FOO = "foo":

public final class MainKt {
   public static final void main(@NotNull String[] args) {
      Intrinsics.checkParameterIsNotNull(args, "args");
      String var1 = "foo";
      System.out.println(var1);
   }
}

There's no call to Constants.FOO in the second example, the value has been inlined.