Easy Life with Kotlin 😇

Mr. President of Indonesia believe programmer can solve any issue in only 2 weeks(sprint cycle)

somehow quarantine makes me feel not productive especially when I got a lot of projects and should be finished ASAP, so I create some sort of code which is usually used in my side project to simplify and reduce my repetitive code sometime 🤪.

1.Kotlin Extension is function with steroid we can add some Type of data as receiver example

fun Int.multiplyBy(value : Int) : Int = this * value
how to use :
val result = 9.mutiplyBy(8)

or we could enhance variable with lambda

val multiply : (Int , Int) -> Int = { x, y -> x * y}
how to use :
val result = multiply(9,8)

another one used receiver 📡

val multiplyBy : Int.(Int) -> Int = { value -> this * value}
how to use :
val result = 9.multiplyBy(8)

we can chaining one or more function into single LOC.

val plusBy : Int.(Int) -> Int = { value -> this +value}
how to use :
val result = 2.plusBy(1).multiplyBy(10)

⚡ we can easily manipulate any list with high order function, one of my favorite is map .

val orders : List<Order> = listOf(Order(1,”nasgor”,12000),Order(3,”cuangki”,10000)
how to use :
val ordersPrice : List<Int> = orders.map { it.price }

Sealed Class 🦭

It’s like enum class but fancier, we can even make safe execute to guarantee your high-risk function will not get any runtime exception just use some of the try-catch but wrap with sealed class in it.

sealed class Try<out A> {
    data class Failure<out A>(val exception: Throwable) : Try<A>()
    data class Success<out A>(val value: A) : Try<A>()
}
inline operator fun <A> invoke(func: () -> A): Try<A> = try {
    Try.Success(func())
} catch (ex: Throwable) {
    Try.Failure(ex)
}
how to use :
invoke {
   //just run your high risk function here
   getInternalSensorStatus() 
}

Create an extension of your repetitive unit test code it even makes your unit test more readable.

infix fun <T> Subscriber<T>.`hasValue`(value : T?) {
   //add your repetitive code here
   assertComplete()
   assertNoError()
   assertValueCount(1)
   assertValue(value)
}
how to use :
@Test
fun TestMySubsriberHasValue{
    someSubscriber `hasValue` expectedValue
}

make webserver test more readable with kotlin extension stuff and of course reduce repetitive code.

enum class HttpMethod {
  DELETE,GET,POST,PUT,PATCH
}
enum class ContentType(val type : String) {
  FORM_URL_ENCODED("xxx-form-url-encoded")
  JSON("json-type")
}
data class ExpectedRequest{
  authorization : String?,
  method : HttpMethod?,
  contentType : ContentType?,
  path : String?,
  body : String?
}
infix fun `received request`(expectedReq : ExpectedRequest){
  val actualReq : MyRequest = this.takeRequest()
  actualReq `is valid` actualReq.authorization
  other checking value, etc...
}
infix fun MyRequest.`is valid`(value : String){
  this.getHeader("Authorization") `should equal` value
}
infix fun <T> T.`should equal`(expected : T) : T = this.apply{         
  assertEqual(expected,this)
}
how to use : 
mockWebserver `received request` ExpectedRequest(
   authorization = "BEARER SECURE_TOKEN",
   method = POST,
   contentType = JSON,
   path = "/evm/search/query",
   body = """{ "product" : "celana kulot cantik pisan", "size" : 
   "L"}"""
)

Operator Overloading

operator fun CompositeDisposable.plusAssign(disposable : Disposable{
 add(disposable)
}
how to use :
fun searchModel(query :String){
compositeDisposable += repository.searchModel(query).subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(::doAction)
}

Bundle Delegate it’s very useful for any lazy developer write key for fragment instance

class StringBundleDelegate{
   operator fun getValue(
      bundle : Bundle,
      property : KProperty<*>
   ):String {
    return bundle.getString(property.name)     
   }
   operator fun setValue(
      bundle : Bundle,
      property : KProperty<*>,
      value : String?){
        bundle.putString(property.name)     
      }
}

val Bundle.Title : String? by StringBundleDelegate()
val Bundle.Id : String? by StringBundleDelegate()
fun newInstanceFragmentHome(title : String,catalogId : String) : HomeFragment{
   val bundle = Bundle()
   bundle.Title = title
   bundle.Id = catalogId
   return HomeFragment().also{
   arguments = bundle
 }
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?){
   dataBinding.appbar.title = arguments?.Title
   arguments?.Id?.let { id ->
    viewModel.getCatalogId(id)
   }
}

you can read more trick here : https://kotlinlang.org/docs/reference/android-overview.html