What is the best way to define log TAG constant in Kotlin?

Question

I'm creating my first Kotlin classes in my Android application. Usually for logging purposes I have a constant with name TAG. What I would do in Java is:

private static final String TAG = MyClass.class.getSimpleName();

I know that in Kotlin classes I can create TAG using this way:

private val TAG = MyClass::class.java.simpleName

This is OK for projects that use Java and Kotlin but what if I start a new project that is only in Kotlin? How can I define there TAG constant? Is there more Kotlin way where I don't have this strange construction class.java.simpleName?

Answer 1

This extension allows us to use TAG in any class

val Any.TAG: String
    get() {
        val tag = javaClass.simpleName
        return if (tag.length <= 23) tag else tag.substring(0, 23)
    }

//usage
Log.e(TAG,"some value")

It it also validated to work as an Android valid Log tag.

Answer 2

In general constants are all caps (ex. FOO) and located in the companion object:

class MyClass {
    companion object {
        public const val FOO = 1

    }
}

and to define the TAG field you can use:

private val TAG = MyClass::class.qualifiedName

Answer 3

Commonly suggested approach of using the companion object generates extra static final instance of a companion class and thus is bad performance and memory-wise.

The best way (IMHO)

Define a log tag as a top-level constant, thus only extra class is generated (MyClassKt), but compared to companion object there will be no static final instance of it (and no instance whatsoever):

private const val TAG = "MyLogTag"

class MyClass {

    fun logMe() {
        Log.w(TAG, "Message")
    }
}

Another option

Use a normal val. Though this looks unusual to see a log tag not as an all-uppercase constant, this will not generate any classes and has least overhead.

class MyClass {

    private val tag = "myLogTag"

    fun logMe() {
        Log.w(tag, "Message")
    }
}