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:

Answer 1

Here is my extension function in kotlin, just add it in your extensions file.

val Any.TAG: String
get() {
    return if (!javaClass.isAnonymousClass) {
        val name = javaClass.simpleName
        if (name.length <= 23 || Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) name else
            name.substring(0, 23)// first 23 chars
    } else {
        val name = javaClass.name
        if (name.length <= 23 || Build.VERSION.SDK_INT >= Build.VERSION_CODES.N)
            name else name.substring(name.length - 23, name.length)// last 23 chars
    }
}

Then you can use TAG in any class like below:

Log.d(TAG, "country list")

Answer 2

In Kotlin you could create an extension, and call tag as a method call instead. This would mean you'd never have to define it inside each class, we can construct it dynamically each time we call the method:

inline fun <reified T> T.TAG(): String = T::class.java.simpleName

Answer 3

I Like TAG to be an extension function as suggested by Fredy Mederos.

extending his answer to support anonymous classes :

 /**
 * extension function to provide TAG value
 */
val Any.TAG: String
    get() {
        return if (!javaClass.isAnonymousClass) {
            val name = javaClass.simpleName
            if (name.length <= 23) name else name.substring(0, 23)// first 23 chars
        } else {
            val name = javaClass.name
            if (name.length <= 23) name else name.substring(name.length - 23, name.length)// last 23 chars
        }
    }

Answer 4

In Android Studio, the usual way to rename something is to right-click the name, select Refactor->Rename. So, I think it's fine to do something like this,

class MyClass {
    companion object {
        private const LOG_TAG = "MyClass"
    }
}

because if you rename the class MyClass like I described, then the IDE will suggest renaming your LOG_TAG String as well.

Ultimately there are pros and cons of using this method vs. other methods. Because LOG_TAG is a String, there's no need to import the kotlin-reflect.jar, as you would if you set LOG_TAG equal to MyClass::class.simpleName. Also because the variable is declared as a compile-time constant with the const keyword, the generated bytecode is smaller since it doesn't need to generate more hidden getters, as described in this article.

Answer 5

I found a way which is more "copy-paste"-able, since it doesn't require you to type the name of your class:

package com.stackoverflow.mypackage

class MyClass
{
    companion object {
        val TAG = this::class.toString().split(".").last().dropLast(10)
    }
}

It's not the most elegant solution but it works.

this::class.toString().split(".").last() will give you "com.stackoverflow.mypackage.MyClass$Companion" so you need the dropLast(10) to remove $Companion.

Alternatively you can do this:

package com.stackoverflow.mypackage

class MyClass
{
    val TAG = this::class.simpleName
}

But then the TAG member variable is no longer "static" and doesn't follow the recommended naming conventions.

Answer 6

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