While writing DSL in Kotlin for an API with lots of classes I'd encountered an issue. Code seemed completely boilerplate to me. Is there a way to generalize code in DSL builders?
Suppose we have an API:
class Robot(val name: String, val head: Head, val body: Body, val hands: Hands, ...)
class Head(val mouth: Mouth, ... )
class Body(val material: Material, ... )
class Hands(...)
class Mouth(...)
class Material(...)
The classes dependency tree could be much larger than that.
DSL for this api would look something like:
fun robot(name: String, settings: RobotBuilder.() -> Unit) = RobotBuilder(name).apply(settings).build()
interface Builder<T> {
fun build(): T
}
#RobotDsl
class RobotBuilder(val name: String) : Builder<Robot> {
private var head: Head = DefaultBotParts.head
private var body: Body = DefaultBotParts.body
private var hands: Hands = DefaultBotParts.hands
...
fun head(initHead: HeadBuilder.() -> Unit) {
head = HeadBuilder().apply(initHead).build()
}
fun body(initBody: BodyBuilder.() -> Unit) {
body = BodyBuilder().apply(initBody).build()
}
fun hands(initHands: HandsBuilder.() -> Unit) {
body = HandsBuilder().apply(initHands).build()
}
...
override fun build(): Robot = Robot(name, head, hands)
}
#RobotDsl
class HeadBuilder : Builder<Head> {
private var mouth: Mouth = DefaultBotParts.mouth
fun mouth(init: MouthBuilder.() -> Unit) {
mouth = Mouth().apply(init).build()
}
override fun build(): Robot = Head(mouth)
}
#RobotDsl
class MouthBuilder : Builder<Mouth> {
//its properties and dsl functions
...
override fun build(): Mouth = Mouth(...)
}
I think the problem is clear now. Each builder can have one or more dependent ones, and they only needed for declaring dsl functions and scope separation, the code is boilerplate.
So, can there be a simple solution that generalizes the code?
Related
Im new to Kotlin and investigating what is/isnt possible
I have a use case as follows:-
As a technical exercise I am attempting to model remote API requests and responses, and enforce relationships between them
My goal is to be able to declare the relationship between Requests and Responses in a clear and succinct way at the top of a Class. This will 1). document the API calls made by this Class, 2). Enforce the relationship so that Request1 can only produce Response1
Pseudo code:-
Requests {
Request1 -> Response1
Request2 -> Response2
...
RequestN -> ResponseN
}
I have defined two interfaces Request & Response and employ them as follows:-
interface Request {
fun <T> response(data : T): Lazy<Response>
}
interface Response
data class Request1(val request: String) : Request {
data class Response1(val output: String) : Response
override fun <T> response(data: T): Lazy<Response> {
return lazy { Response1(data as String) }
}
}
data class Request2(val request: Long) : Request {
data class Response2(val output: Double) : Response
override fun <T> response(data: T): Lazy<Response> {
return lazy { Response2(data as Double) }
}
}
I have a Controller class that makes the API calls as follows:-
class Controller {
fun call(request: Request): Lazy<Response> {
return when (request) {
is Request1 -> request.response("Testing Data")
is Request2 -> request.response(Math.PI)
else -> TODO()
}
}
}
Using the above data classes I can enforce that Request1 is linked to only Response1 and also specify the response data type wrapped by each Response.
Although the above classes provide the functionality and adhere to these rules, they are verbose.
Is there a more succinct approach I could employ to obtain the desired result.
The reason I require this is I am looking for "Self Documenting" code, where a developer can view the definition of Request/Response pairs and association rules and clearly see what is intended.
For example: A developer looking at the final Request definitions can clearly see that Response1 with be generated by Request1. I also want to enforce that Response1 can only ever be produced from Request1.
My example above is simplified, as in "The Real World" the data wrapped by each Response will be sourced from the actual API request call, I have illustrated with "Hard Coded".
I would much rather define Request1 and Response1 on a single line if possible.
UPDATE
I have refactored my original classes as follows:-
interface Request<ResponseData> {
fun response(data: ResponseData): Lazy<Response>
}
interface Response
sealed class Requests<T> : Request<T> {
data class Request1(val request: String) : Requests<String>() {
inner class Response1(val output: String) : Response
override fun response(data: String): Lazy<Response> {
return lazy { Response1(data) }
}
}
data class Request2(val request: Long) : Requests<Double>() {
inner class Response2(val output: Double) : Response
override fun response(data: Double): Lazy<Response> {
return lazy { Response2(data) }
}
}
}
class Controller {
fun <T> call(request: Request<T>): Lazy<Response> {
return when (request) {
is Requests.Request1 -> request.response("Testing Data")
is Requests.Request2 -> request.response(Math.PI)
else -> TODO()
}
}
}
While this version of my code has many benefits from the original, one feature I am still not happy with is that each Request/Response declaration is still quite verbose, e.g. it requires 5 lines of code. Is there an approach I can employ to make each Request/Response pair declaration more succinct?, e.g. take up fewer lines of code.
UPDATE II
Im attempting to refactor my sealed class above so that the overridden function response is defined in the outer sealed class.
interface Request<ResponseData> {
fun response(data: ResponseData): Lazy<Response>
}
interface Response
sealed class Requests<T> : Request<T> {
data class Request1(val request: String) : Requests<String>() {
inner class Response1(val output: String) : Response
}
data class Request2(val request: Long) : Requests<Double>() {
inner class Response2(val output: Double) : Response
}
override fun response(data: T): Lazy<Response> {
return lazy { // What implementation goes here??? // }
}
}
Is this approach possible?
How do I refer to the individual concrete ResponseN classes in the outer sealed class?
Another approach:
data class Box<T, V>(val req: T, val rsp: V)
interface Interaction<RequestT, ResponseT> {
val req: RequestT
fun exec(): Box<RequestT, ResponseT>
}
sealed class Interactions<RequestT, ResponseT> : Interaction<RequestT, ResponseT> {
class Interaction1(override val req: String) : Interaction<String, String> {
override fun exec() = Box(req, "by")
}
class Interaction2(override val req: Long) : Interaction<Long, Double> {
override fun exec() = Box(req, 1.0)
}
}
fun main() {
val interaction1 = Interactions.Interaction1("hi")
val interaction2 = Interactions.Interaction2(42)
println(interaction1.exec()) // Box(req=hi, rsp=by)
println(interaction2.exec()) // Box(req=42, rsp=1.0)
}
Maybe your example is simplified from what you're actually doing, but I don't see the purpose of the Response interface, or the need for separate Request implementations to achieve what your code does:
data class Request<T>(val request: String, val responseType: KClass<out T>) {
fun response(data : T) = lazy { data }
}
class Controller {
fun <T: Any> call(request: Request<T>): Lazy<T> {
#Suppress("UNCHECKED_CAST")
return when (request.responseType) {
String::class -> request.response("Testing Data" as T)
Double::class -> request.response(Math.PI as T)
else -> TODO()
}
}
}
It's kind of an odd use of Lazy though, since you are wrapping a pre-computed value.
My goal is to be able to declare the relationship between Requests and Responses in a clear and succinct way at the top of a Class. This will 1). document the API calls made by this Class, 2). Enforce the relationship so that Request1 can only produce Response1
A great way to enforce the relationships is to separate the interface and implementation levels. Currently you have your interface defined as
interface Request {
fun <T> response(data : T): Lazy<Response>
}
And it does not tell you that the response can vary. It's high level and then you define actual relations in your implementation.
I suggest to decouple relations and the implementation by moving the relations to the interface level.
Here is my suggestion. Forgive me if something does not compile, I'm writing the code from my head, I want to communicate the design ideas and you may have to change some pseudocode.
Let's start with the interface:
interface Response
interface Request // I see that you are using primitive types for requests, so you don't need the interface. But in a real world scenario your requests will probably be more complex than primitive types and then it will make sense to wrap them in this interface. It also makes the code easier to understand - a string can be anything, while a Request is definitely a request.
// This is an interface that actually performs a request, so makes sense to name it in an actionable way
interface Requester<T, M> {
fun <in T: Request, out M: Response> request(data : T): Lazy<M>
}
This declaration tells you that there are different kinds of requests and responses and that there are some relations, but do not say what relations are yet.
Then I would declare the responses and requests implementations in a separate place to keep this code short and to the point
class Request1(val input: String) : Request
class Request2(val input: Double) : Request
class Response1(val output: String) : Response
class Response2(val output: Double) : Response
Then you declare the actual relations
interface Requester1: Requester<Request1, Response1>
interface Requester2: Requester<Request2, Response2>
At this point you have a file that clearly communicates the relation without any implementation details.
This is you final interface code, that solves your request for 1). document the API calls made by this Class, 2). Enforce the relationship so that Request1 can only produce Response1 ⬇️
interface Response
interface Request
interface Requester {
fun <in T: Request, out M: Response> request(data : T): Lazy<M>
}
interface Requester1: Requester<Request1, Response1>
interface Requester2: Requester<Request2, Response2>
Then you can do the implementation in a separate place to keep the interface clean and easy to understand.
sealed class Requests {
data class RequesterImpl1(val request: String) : Requests, Requester1 {
override fun request(data: Request1): Lazy<Response1> {
return lazy { Response1(data) }
}
}
data class RequesterImpl2(val request: Long) : Requests, Requester2 {
override fun request(data: Double2): Lazy<Response2> {
return lazy { Response2(data) }
}
}
}
This is the current design I am using
fun doNothing(): Unit = Unit
interface Interaction<Input, Output> {
interface Response<Output> : Interaction<Unit, Output> {
val output: Output
}
interface Request<Input, Output> : Interaction<Input, Output> {
val input: Input
fun react(output: Output): Response<Output>
}
}
sealed class Interactions<I, O> : Interaction<I, O> {
data class RequestOne(override val input: String) : Interaction.Request<String, Long> {
internal data class ResponseOne(override val output: Long) : Interaction.Response<Long>
override fun react(output: Long): Interaction.Response<Long> = ResponseOne(output)
}
data class RequestTwo(override val input: CustomInput) : Interaction.Request<CustomInput, CustomOutput> {
internal data class ResponseTwo(override val output: CustomOutput) : Interaction.Response<CustomOutput>
override fun react(output: CustomOutput): Interaction.Response<CustomOutput> = ResponseTwo(output)
}
data class RequestThree(override val input: Unit = doNothing()) : Interaction.Request<Unit, CustomOutputTwo> {
internal data class ResponseThree(override val output: CustomOutputTwo) : Interaction.Response<CustomOutputTwo>
override fun react(output: CustomOutputTwo): Interaction.Response<CustomOutputTwo> = ResponseThree(output)
}
data class RequestFour(override val input: Unit = doNothing()) : Interaction.Request<Unit, Unit> {
internal data class ResponseFour(override val output: Unit = doNothing()) : Interaction.Response<Unit>
override fun react(output: Unit): Interaction.Response<Unit> = ResponseFour()
}
data class RequestFive(override val input: CustomInputTwo) : Interaction.Request<CustomInputTwo, Unit> {
internal data class ResponseFive(override val output: Unit = doNothing()) : Interaction.Response<Unit>
override fun react(output: Unit): Interaction.Response<Unit> = ResponseFive()
}
}
I believe this approach enforces the relationships I require between individual Requests and their associated Response types.
The features of this design I would like to improve on is the use of Unit when defining the Response interface.
Also I cannot see a way to improve on the sealed class Interactions<I, O> : Interaction<I, O> {...}, as I never use the Generic I & O
I would also like to be able to define a single fun react(output: Output): Response<Output> within the parent sealed class Interactions instead of having to implement this function in each inner Action data class, however I do not think that is possible.
Consider the following function:
abstract class ObservableCollection<E> : CoroutineScope, MutableCollection<E> {...}
class ObservableList<E>(override val backingSource: MutableList<E> = mutableListOf()) : ObservableCollection<E>(), MutableList<E> by backingSource {...}
inline fun <reified T : Event<E>, E> ObservableCollection<E>.on(scope: CoroutineScope = this, noinline consumer: suspend (T) -> Unit): Job =
events.buffer(Channel.UNLIMITED)
.filterIsInstance<T>().onEach {
runCatching { consumer(it) }.onFailure { ObservableCollection.logger.catching(it) }
}.catch { ObservableCollection.logger.catching(it) }
.launchIn(scope)
To call it, the first and general way (which comes in mind):
val list = ObservableList<Int>()
list.on<ElementAddEvent<Int>, Int> {
}
To make it more idiomatic (towards removing redundancy of passing explicit generics), we can have something like this:
list.on { event: ElementAddEvent<Int> ->
}
But is there a way to remove that explicit generic type <Int> in { event: ElementAddEvent<Int> -> as well? Since it is implicit, as coming from the type of ObservableList on which on method/function is called on.
Edit:
Event<E> is basically an interface to for all the possible events like ElementRemoveEvent<E>, ElementAddEvent<E>, ElementReplaceEvent etc.
interface Event<E> : CoroutineScope {
override val coroutineContext: CoroutineContext
get() = collection.coroutineContext
val collection: ObservableCollection<E>
}
class ElementAddEvent<E>(
val element: E,
override val collection: ObservableCollection<E>
) : Event<E>
class ElementReplaceEvent<E>(
val newElement: E,
val oldElement: E,
override val collection: ObservableCollection<E>
) : Event<E>
// And so-on...
It has basically nothing to do with the question, so I didn't put it on.
Edit 2:
One way could be to make static functions in each of the event like:
class ElementAddEvent<E>(
val element: E,
override val collection: ObservableCollection<E>
) : Event<E> {
companion object {
fun <E> on(collection: ObservableCollection<E>, consumer: suspend (ElementAddEvent<E>) -> Unit) {
collection.on { event: ElementAddEvent<E> ->
consumer(event)
}
}
}
}
This will make possible to be callable as:
ElementAddEvent.on(list) {
}
But I think this will make too much noise in the sources, so I would prefer to use the second approach posted in the question itself (specifying type inside the lambda). If I missed something question is still open, you can let me know!
Say I have this situation:
interface Repository {
fun getMovies(success: (List<String>) -> Unit, failure: (Int) -> Unit)
}
and I want to mock the implementation of this interface. Basically in this case, there are two lambdas as input parameters to the getmovie method, and for the test case, I only want to produce success (success.invoke(theMoviesList) should be called).
Below is something similar to what I would like to do:
class MovieViewModel constructor(val repository: AppRepository) {
var movieNames = listOf<String>() // Not private, or live data, for simplicity
fun fetchMovies() {
repository.fetchMovies(
success = {
movies ->
this.movieNames = movies
}}, failure: {
statusCode ->
})
}
}
class MoviePageTests {
private var movieViewModel: MovieViewModel? = null
#Mock
lateinit var mockRepository: AppRepository
#Before
#Throws(Exception::class)
fun before() {
MockitoAnnotations.initMocks(this)
movieViewModel = MovieViewModel(repository = mockRepository)
}
#Test
fun checkFetchMoviesUpdatesMoviesData() {
var testMovies = listof("Dracula", "Superman")
//Set up mockito so that the repository generates success with testMovies above
?????
//
movieViewModel.fetchMovies()
assertEquals(movieViewModel.movies, testMovies)
}
}
I know how to do this by way of a RepositoryImpl, but not in Mockito, despite looking at many examples online.
Any ideas?
I have a class that receives a function allowing it to display things on the UI during a failure case. What's the best way that I can verify that the function is called in my test?
MyClass(private val uiPrinter: (String) -> Unit) {
fun foo() {
// do some stuff
uiPrinter("printing from foo!")
// do some more stuff
}
}
MyClassTest() {
val testUiPrinter: (String) -> Unit = { System.out.println(it) }
#Test
fun uiPrinterIsInvoked() {
val myClass = MyClass(testUiPrinter)
myClass.foo()
// can I verify that testUiPrinter has been invoked?
}
}
You may want to check out the Model-View-Presenter architecture. Its purpose is to hide the Android framework behind an abstract View interface which a purely Java Presenter can interact with. In your example:
interface ViewInterface {
fun printError(error: String)
}
class MyPresenter(private val view: ViewInterface) {
fun foo() {
// do some stuff (testable stuff)
view.printError("Printing from foo()!")
// do some more (testable) stuff
}
}
class MyPresenterTest() { // Test using Mockito to mock the abstract view
private val view = mock(ViewInterface::class.java)
private val presenter = MyPresenter(view)
#Test
fun printsError() {
// set up preconditions
presenter.foo()
verify(view).printError("Printing from foo()!")
}
}
Your concrete view will generally be an Android Activity, Fragment, or View which implements the view interface. Notice MyPresenter only expects the abstract view and does not need knowledge of the framework-dependent operations.
class MyActivity : Activity(), ViewInterface {
// ...
override fun printError(error: String) {
textView.text = error // For example
}
// ...
}
This can be achieved by mocking the higher-order function as higher-order functions are objects unless inlined.
#Mock
val testUiPrinter: (String) -> Unit
#Test
fun uiPrinterIsInvoked() {
val myClass = MyClass(testUiPrinter)
myClass.foo()
verify(testUiPrinter).invoke("Printing from foo!")
}
I am trying to implement a QueryBus. Basically, I want to register a list of QueryHandlers. Each QueryHandler implements a handle method defined by an interface. Each QueryHandler is associated to a Query. I want to be able to retrieve a QueryHandler using the Query and call handle on it.
The thing is the handle has to be generic because each QueryHandler handles a Query differently. They all take a dedicated Query and may return whatever they want.
interface Query<R>
interface QueryHandler<R, Q : Query<R>> {
fun handle(query: Q): R
fun listenTo(): String
}
// DTOs
data class BookDto(val name: String)
// List books query
data class ListBooksQuery(val page: Int = 1): Query<List<BookDto>>
class ListBooksQueryHandler: QueryHandler<List<BookDto>, ListBooksQuery> {
override fun handle(query: ListBooksQuery): List<BookDto> {
return listOf(BookDto("Dune"), BookDto("Dune II"))
}
override fun listenTo(): String = ListBooksQuery::class.toString()
}
// Get book query
data class GetBookQuery(val name: String): Query<BookDto?>
class GetBookQueryHandler: QueryHandler<BookDto?, GetBookQuery> {
override fun handle(query: GetBookQuery): BookDto {
return BookDto("Dune")
}
override fun listenTo(): String = GetBookQuery::class.toString()
}
// Run it!
fun main(args: Array<String>) {
// Initializing query bus
val queryHandlers = mapOf(
with(ListBooksQueryHandler()) {this.listenTo() to this},
with(GetBookQueryHandler()) {this.listenTo() to this}
)
val command = ListBooksQuery()
val result = queryHandlers[command::class.toString()].handle(command)
// Should print the list of BookDto
print(result)
}
I don't even know if its possible, to be honest.
UPDATE 1:
I changed the usage example in the main to show what I am really trying to do. The List was for (bad?) demonstration purpose. I want to store the QueryHandlers and retrieve them from a map.
Additional resources:
Here is what I really want to do:
https://gist.github.com/ValentinTrinque/76b7a32221884a46e657090b9ee60193
UPDATE I've read your gist and tried to come up with a solution that will provide a clean interface to the user of the QueryBusMiddleware.
Note that I used objects instead of classes for the QueryHandler implementations, which felt more natural to me (since there is only one possible entry in the map for each Query implementation).
interface Query<R>
interface QueryHandler<R, Q: Query<R>> {
fun handle(query: Q): R
fun listenTo(): String
}
// DTOs
data class BookDto(val name: String)
// List books query
data class ListBooksQuery(val page: Int = 1): Query<List<BookDto>>
object ListBooksQueryHandler: QueryHandler<List<BookDto>, ListBooksQuery> {
override fun handle(query: ListBooksQuery): List<BookDto> {
return listOf(BookDto("Dune"), BookDto("Dune II"))
}
override fun listenTo(): String = ListBooksQuery::class.toString()
}
// Get book query
data class GetBookQuery(val name: String): Query<BookDto?>
object GetBookQueryHandler: QueryHandler<BookDto?, GetBookQuery> {
override fun handle(query: GetBookQuery): BookDto {
return BookDto("Dune")
}
override fun listenTo(): String = GetBookQuery::class.toString()
}
// Run it!
fun main(args: Array<String>) {
// Initializing query bus
val queryHandlers = listOf(
ListBooksQueryHandler,
GetBookQueryHandler
)
val dispatcher: QueryBusMiddleware = QueryDispatcherMiddleware(queryHandlers)
// Calling query bus
val query = ListBooksQuery()
// Result should be List<BookDto>
val result = dispatcher.dispatch(query)
print(result)
}
interface QueryBusMiddleware {
fun <R, Q : Query<R>> dispatch(query: Q): R
}
class QueryDispatcherMiddleware constructor(handlers: List<QueryHandler<*, *>>) : QueryBusMiddleware {
private val handlers = HashMap<String, QueryHandler<*, *>>()
init {
handlers.forEach { handler -> this.handlers[handler.listenTo()] = handler }
}
override fun <R, Q : Query<R>> dispatch(query: Q): R {
val queryClass = query::class.toString()
val handler = handlers[queryClass] ?: throw Exception("No handler listen to the query: $queryClass")
return handler::class.members.find { it.name == "handle" }!!.call(handler, query) as R
}
}