skiedrowski/flavourit

A Kotlin Annotation Processor (kapt) Proof of Concept for flavouring (@Fork)

A flavouring proof-of-concept using Kotlin Annotation Processing (kapt)

Idea

• Provide a Fork annotation which specifies which method should be forked to which method on which flavour.
• Generate new kotlin code implementing the delegating method as an extension function to the class.

Usage

Implement the class acting as a fork target:

package com.github.skiedrowski.flavourit

@Forks(
    [
        Fork(from = "delegator1", to = "toEsa1", ifActive = "Esa"),
        Fork(from = "delegator1", to = "toRoskosmos1", ifActive = "Roskosmos"),
        Fork(from = "delegator2", to = "toEsa2", ifActive = "Esa")
    ]
)
class MultipleForks() {

    internal fun toRoskosmos1() {
        println("Running Roskosmos 1")
    }

    internal fun toEsa1() {
        println("Running Esa 1")
    }

    internal fun toEsa2() {
        println("Running Esa 2")
    }

}

Specify the current flavour in build.gradle:

kapt {
	arguments {
		arg("flavourit.flavour", "Esa")
	}
}

It should be possible to specify the flavour somewhere else (command line, another gradle task, gradle.properties, ...).

Run the build

./gradlew clean build

During compilation, kapt scans for Fork and Forks annotations and creates a new File MultipleForksExt.kt containing the delegates:

package com.github.skiedrowski.flavourit

fun MultipleForks.delegator1() {
	println("MultipleForksExt: delegating from: delegator1 - to: toEsa1 - because of flavour: Esa")
	toEsa1()
}

fun MultipleForks.delegator2() {
	println("MultipleForksExt: delegating from: delegator2 - to: toEsa2 - because of flavour: Esa")
	toEsa2()
}

Run a test program

If a client (AForkMeClient) calls delegator1() or delegator2(), it'll be delegated to the implementations specified using the Fork annotations.

fun main(args: Array<String>) {
	val multipleForks = MultipleForks()
	println("calling delegator1")
	multipleForks.delegator1()
	println("calling delegator2")
	multipleForks.delegator2()
} 

Output:

calling delegator1
MultipleForksExt: delegating from: delegator1 - to: toEsa1 - because of flavour: Esa
Running Esa 1
calling delegator2
MultipleForksExt: delegating from: delegator2 - to: toEsa2 - because of flavour: Esa
Running Esa 2