dananas/no-exclamations

Android Lint rule that forbids kotlin !! operator

No exclamations!!

This is an Android lint rule that forbids the use of the !! operator in Kotlin.

How to use it

Import with gradle:

repositories {
    maven {
        url  "https://dl.bintray.com/dananas/android" 
    }
}

dependencies {
    lintChecks "com.github.dananas:no-exclamations:0.1.0"
}

The code won't compile if abortOnError is set to true.

android {
    lintOptions {
        abortOnError true
    }
}

Why !! is bad

Unlike Java, Kotlin natively supports nullable types. By using !! not only you throw away this functionality, your code becomes error prone and sometimes non-obvious, because one needs to know the whole lifecycle of the instances !! was used for.

Consider using TheGood way:

class TheGood {
    private var name: String? = null
    fun setup() {
        name = "Clint Eastwood"
    }
    override fun toString(): String {
        return requireNotNull(name) { "Name is not set!" }
    }
}

class TheBad {
    private var name: String? = null
    fun setup() {
        name = "Lee Van Cleef"
    }
    override fun toString(): String {
        return name!!
    }
}

class TheUgly {
    private lateinit var name: String
    fun setup() {
        name = "Eli Wallach"
    }
    override fun toString(): String {
        return name
    }
}

License

Apache-2.0