I was wondering - what is the best way to mock Kotlin's receivers? In more concrete terms, let's say I defined the following interfaces:
interface TransactionalRepository {
fun <T> withTransaction(TransactionalOperations.() -> T)
}
interface TransactionalOperations {
fun <T: Entity> save(entity: T)
fun <T: Entity> load(id: UUID): T
}
Assuming I have some business logic using an implementation of TransactionalRepository like this:
fun decrementCounter(counterId: UUID) {
repository.transaction {
val entity: Counter = load(counterId)
entity.decrement()
save(entity)
}
}
What is the best way to mock out the interactions between TransactionalRepository and TransactionalOperations?
Related
I am trying to implement a generic HttpClient like this one:
interface HttpClient {
fun <T: Any> get(url: String): T?
}
implemented by a class like this:
class HttpClientImpl #Inject constructor(...) : HttpClient {
override fun <T : Any> get(url: String): T? = execute(url)
private inline fun <reified T: Any> execute(url: String): T? {
val request = Request.Builder().url(url).get().build()
client.newCall(request).execute().use {
return it.body?.parseBodySuccess()
}
}
private inline fun <reified T: Any> ResponseBody?.parseBody(): T? {
val type = objectMapper.typeFactory.constructType(T::class.java)
return this?.let { objectMapper.readValue(it.string(), type) }
}
}
Now, I would like to be able to call such GET method in this way:
data class MyEntity(...)
class MyService #Inject constructor(private val client: HttpClient) {
fun performGet(url: String): MyEntity? = client.get<MyEntity>(url)
}
However this is not allowed and the compiler throws an error referring to the line of code
override fun <T : Any> get(endpoint: String): T? = execute(endpoint)
flagging that : Cannot use 'T' as reified type parameter. Use a class instead.
I have been trying to re-write the line as
override inline fun <reified T : Any> get(endpoint: String): T? = execute(endpoint)
however, despite having to make the other two inline functions "non private" the compiler still won't compile because in this last way of writing the overriding function, it says:
Override by a function with reified type parameter
How can I achieve such generic function?
I ended up doing something like this:
interface HttpClient {
fun <T: Any> get(url: String, type: Class<T>): T?
}
implemented as:
class HttpClientImpl #Inject constructor(...) : HttpClient {
override fun <T : Any> get(url: String, type: Class<T>): T? = execute(url, type)
private fun <T: Any> execute(url: String, type: Class<T>): T? {
val request = Request.Builder().url(url).get().build()
client.newCall(request).execute().use {
return it.body?.parseBody(type)
}
}
private fun <T: Any> ResponseBody?.parseBody(type: Class<T>): T? {
val dataType = objectMapper.typeFactory.constructType(type)
return this?.let { objectMapper.readValue(it.string(), dataType) }
}
}
that I can call in this way:
data class MyEntity(...)
class MyService #Inject constructor(private val client: HttpClient) {
fun performGet(url: String): MyEntity? = client.get(url, MyEntity::class.java)
}
I would have preferred to pass the Type directly as an actual type like
client.get<MyEntity>(url)
rather than passing the Class as a parameter, however, just for now it works...
If anyone can suggest a better way of doing this, please let me know.
Updated
As suggested by Pawel, I have created an extra inline extension function to the HttpClient interface
inline fun <reified T:Any> HttpClient.get (url: String) = get(url, T::class.java)
And I'm now able to call the function the way I wanted.
I have this sealed class
sealed class S3FileUploaderRequest {
abstract val s3Configuration: S3Configuration
data class S3UploadRequest(
val uploadData: S3UploadData,
override val s3Configuration: S3Configuration
) : S3FileUploaderRequest()
data class S3DeleteRequest(
val path: String,
override val s3Configuration: S3Configuration
) : S3FileUploaderRequest()
data class S3MultiUploadRequest(
val multiUploadData: List<S3UploadData>,
override val s3Configuration: S3Configuration
) : S3FileUploaderRequest()
data class S3MultiDeleteRequest(
val paths: List<String>,
override val s3Configuration: S3Configuration
) : S3FileUploaderRequest()
}
And this interface:
interface FileUploader<T, S> {
suspend fun multiUploadFile(request: T): S
suspend fun multiDeleteFile(request: T): List<S>
suspend fun uploadFile(request: T): S
suspend fun deleteFile(request: T): S
}
I would like to use the child classes of data class S3FileUploaderRequest es entry parameter of interface functions, somethig like this:
interface FileUploader<T, S> {
suspend fun multiUploadFile(request: out T): out S
suspend fun multiDeleteFile(request: out T): List<S>
suspend fun uploadFile(request: out T): out S
suspend fun deleteFile(request: out T): out S
}
Is possible to do this? I feel like kotlin should be able to do this but don't find the proper syntax for it.
Update:
I would like to implement the interface this way:
#Singleton
class S3FileUploader() : FileUploader<S3FileUploaderRequest, S3FileUploaderResponse> {
override suspend fun uploadFile(request: S3UploadRequest): S3UploadResponse {
//DO STUFF
}
override suspend fun deleteFile(request: S3DeleteRequest): S3DeleteResponse {
//DO STUFF
}
override suspend fun multiUploadFile(request: S3MultiUploadRequest): S3MultiUploadResponse {
//DO STUFF
}
override suspend fun multiDeleteFile(request: S3MultiDeleteRequest): List<S3DeleteResponse> {
//DO STUFF
}
}
I want to return T in the function.
I have an interface class IRepository.kt
interface IRepository
{
fun <T>Save(model:T)
fun <T>Delete(model:T)
fun <T>Get(id:Long):T
}
I want to implement in Repolmpl.kt
class Repolmpl:IRepository
{
override fun <T>Delete(model:T)
{
println("$model : Save}")
}
override fun <T>Get(id:Long):T
{
return T //ERROR here I want to return T...
}
override fun <T> Save(model: T)
{
println("$model : Delete")
}
}
I saw some similar questions online but I just can't find the right solution.
A generic type T is basically just a template. You cannot return it but have to replace it with an actual type first. Make the interface itself generic, not its methods. When implementing, specify T:
interface IRepository<T> {
fun save(model: T)
fun delete(model: T)
fun get(id: Long): T
}
class Repolmpl: IRepository<String>
{
override fun delete(model: String) {}
override fun get(id: Long): String {}
override fun save(model: String) {}
}
You cannot just return T. T is type here, and it is like return String.
You have to return instance of T. So, sth like:
class Repo {
val data = mapOf<Long, Any>()
// ...
fun <T> get(id: Long): T {
return data[id] as T // Get data from somewhere and then cast it to expected type
}
}
I am trying to inherit MutableList, and add my own function to it. For example:
class CompositeJob : MutableList<Job> {
fun cancelAllJobs() {
for (job in this) {
job.cancel()
}
}
}
But I got the following error:
Class 'CompositeJob' is not abstract and does not implement abstract member
public abstract val size: Int defined in kotlin.collections.MutableList
How can I inherit MutableList, so I can use its original methods like add() and isEmpty(), and add my own one?
Thanks.
One option other answers don't mention is delegation:
class CompositeJob : MutableList<Job> by mutableListOf() {
fun cancelAllJobs() {
for (job in this) {
job.cancel()
}
}
}
is basically equivalent to
class CompositeJob : MutableList<Job> {
private val impl: MutableList<Job> = mutableListOf()
override fun size() = impl.size()
override fun add(x: Job) { impl.add(x) }
// etc for all other MutableList methods
fun cancelAllJobs() {
for (job in this) {
job.cancel()
}
}
}
MutableList is an interface - it doesn't implement any of its methods, just declares them. If you want to implement MutableList from scratch, you'll have to implement all 20 of its methods plus the size property, as your error already told you.
You can, however, subclass actual implementations of this interface, for example ArrayList or LinkedList:
class CompositeJob : ArrayList<Job>() {
fun cancelAllJobs() {
for (job in this) {
job.cancel()
}
}
}
Edit: If you're just looking to group coroutine Job instances, you should use a parent Job, a SupervisorJob, and CoroutineScope at this point, instead of collecting jobs like this manually.
Implementation of all the members is not the only way to achieve what you need.
An easier way is create an extension function like this:
fun MutableList<Job>.cancelAllJobs() {
this.forEach { it.cancel() }
}
Now you can call myList.cancelAllJobs() for every MutableList<Job> object.
As I have tested you need to make CompositeJob an abstract as error also suggest. After that, you can able to override add() and isEmpty() from MutableList
So your code looks like as below:
abstract class CompositeJob : MutableList<Job> {
override fun add(element:Job): Boolean
{
}
override fun isEmpty(): Boolean
{
}
}
If you want to avoid inheritance, or if the concrete class methods are marked final, then you can use composition and redirect all method calls which are not overridden. Here's a template:
class MyMutableList<T> : MutableList<T> {
private val list = mutableListOf<T>()
override val size get() = list.size
// MutableList<T>
override fun add(element: T): Boolean = list.add(element)
override fun add(index: Int, element: T) = list.add(index, element)
override fun addAll(elements: Collection<T>): Boolean = list.addAll(elements)
override fun addAll(index: Int, elements: Collection<T>): Boolean = list.addAll(index, elements)
override fun clear() = list.clear()
override fun remove(element: T): Boolean = list.remove(element)
override fun removeAll(elements: Collection<T>): Boolean = list.removeAll(elements)
override fun removeAt(index: Int): T = list.removeAt(index)
override fun retainAll(elements: Collection<T>): Boolean = list.retainAll(elements)
override fun set(index: Int, element: T): T = list.set(index, element)
// List<T>
override fun contains(element: T): Boolean = list.contains(element)
override fun containsAll(elements: Collection<T>): Boolean = list.containsAll(elements)
override fun get(index: Int): T = list.get(index)
override fun indexOf(element: T): Int = list.indexOf(element)
override fun isEmpty(): Boolean = list.isEmpty()
override fun iterator(): MutableIterator<T> = list.iterator()
override fun lastIndexOf(element: T): Int = list.lastIndexOf(element)
override fun listIterator(): MutableListIterator<T> = list.listIterator()
override fun listIterator(index: Int): MutableListIterator<T> = list.listIterator(index)
override fun subList(fromIndex: Int, toIndex: Int): MutableList<T> =
list.subList(fromIndex, toIndex)
}
...of course, this might add an additional layer of indirection, possibly affecting list performance with a slight overhead.
The following is a very simple illustration of what I'm trying to do:
interface Event {
fun value(): Int
}
class Event1: Event {
override fun value() = 1
}
class Event2: Event {
override fun value() = 2
}
interface EventConsumer<T> where T: Event {
fun consume(event: T)
}
class Event1Consumer: EventConsumer<Event1> {
override fun consume(event: Event1) {
println(event.value())
}
}
class Event2Consumer: EventConsumer<Event2> {
override fun consume(event: Event2) {
println(event.value())
}
}
class EventManager {
private val consumers: Map<KClass<*>, EventConsumer<*>> = mapOf(
Event1::class to Event1Consumer(),
Event2::class to Event2Consumer()
)
fun consume(event: Event) {
val consumer = consumers[event::class]
consumer?.consume(event)
}
}
The final method call (consumer.consume()) is giving me a compiler error
Out-projected type 'EventConsumer<*>?' prohibits the use of 'public
abstract fun consume(event: T): Unit defined in EventConsumer'
I know that Kotlin is a lot more strict about generics than Java which is probably why it doesn't work, but how would I implement something like this properly?
Since you are building the consumers map, it would be safe to make an unchecked cast to the correct generic EventConsumer type:
fun <T: Event> consume(event: T) {
val consumer = consumers[event::class] as? EventConsumer<T>
consumer?.consume(event)
}