enum class PackageFlags(val mask: Int) {
    NONE(0), SYSTEM_APP(1), IS_DEBUGGABLE(2), SYSTEM_APP_UPDATED(128), IN_SD_CARD(262144),
    IS_DATA_ONLY(16777216), IS_STOPPED(2097152)
}

The function invoke() is not found

In which case invoke() not found?

Calling

PackageFlags.NONE()

to return its mask value

PackageFlags.NONE.mask

I'm trying make the call a bit cleaner...

operator fun PackageFlags.invoke() = mask