I have a module:
single{ (name: String) -> Person(name) }
When I do:
val alice: Person by inject {parametersOf("Alice")}
val bob: Person by inject {parametersOf("Bob")}
I get 2 instances of Alice. All parameters other than the first are ignored.
Is there a simple way to make Koin treat those 2 as different? Parameters are not known in advance, so I can't use named properties. factory won't do either, I need to reuse instances with same parameter sets.
There is no such thing directly in Koin, but it's easy enough to make something that works this way.
1) a class that does create-if-not-present:
class DistinctFactory<K, V>(private val newInstance: (K) -> V) {
private val _locker = Any()
private val mRepo: HashMap<K, V> = HashMap()
operator fun get(id: K): V {
return mRepo[id] ?: run {
synchronized(_locker) {
mRepo[id] ?: run {
newInstance(id).also {
mRepo[id] = it
}
}
}
}
}
}
2) Koin single of DistinctFactory:
single { DistinctFactory<String, Person> { Person(it) } }
3) Koin factory that uses the previous single:
factory { (name: String) -> get<DistinctFactory<String, Person>>()[name] }
test:
val alice: Person by inject {parametersOf("Alice")}
val bob: Person by inject {parametersOf("Bob")}
val aliceAgain: Person by inject {parametersOf("Alice")}
alice === aliceAgain
module {
val personCache = HashMap<Int, Person>()
factory { parameters ->
val hash = parameters.values.hashCode()
personCache.getOrPut(hash) {
Person(parameters.get())
}
}
}
Related
I have two different pieces of code. In one i need to use object and in the second i'm not.
Can someone explain me the difference between the situation:
first Code:
private val onInitWebResponseHandler: VolleyHandler.WebResponseHandler = VolleyHandler.WebResponseHandler()
{
Thread(ParseJsonStringOnInit(WeakReference(this),
weakRefIOnAllScoresDataFirstFetched, it)).start()
}
Second Code:
val competitionOrderLevelComparator : Comparator<CompetitionObj> = object : Comparator<CompetitionObj> {
override fun compare(object1: CompetitionObj, object2: CompetitionObj): Int
{
return object1.orderLevel - object2.orderLevel
}
}
fun interface WebResponseHandler
{
fun onWebResponseFinished(jsonString:String?)
}
In addition how the first code, we can have () brackets if interface doesn't have a constructor?
I am trying to figure out if I can work with Kotlin and Spark,
and use the former's data classes instead of Scala's case classes.
I have the following data class:
data class Transaction(var context: String = "", var epoch: Long = -1L, var items: HashSet<String> = HashSet()) :
Serializable {
companion object {
#JvmStatic
private val serialVersionUID = 1L
}
}
And the relevant part of the main routine looks like this:
val transactionEncoder = Encoders.bean(Transaction::class.java)
val transactions = inputDataset
.groupByKey(KeyExtractor(), KeyExtractor.getKeyEncoder())
.mapGroups(TransactionCreator(), transactionEncoder)
.collectAsList()
transactions.forEach { println("collected Transaction=$it") }
With TransactionCreator defined as:
class TransactionCreator : MapGroupsFunction<Tuple2<String, Timestamp>, Row, Transaction> {
companion object {
#JvmStatic
private val serialVersionUID = 1L
}
override fun call(key: Tuple2<String, Timestamp>, values: MutableIterator<Row>): Transaction {
val seq = generateSequence { if (values.hasNext()) values.next().getString(2) else null }
val items = seq.toCollection(HashSet())
return Transaction(key._1, key._2.time, items).also { println("inside call Transaction=$it") }
}
}
However, I think I'm running into some sort of serialization problem,
because the set ends up empty after collection.
I see the following output:
inside call Transaction=Transaction(context=context1, epoch=1000, items=[c])
inside call Transaction=Transaction(context=context1, epoch=0, items=[a, b])
collected Transaction=Transaction(context=context1, epoch=0, items=[])
collected Transaction=Transaction(context=context1, epoch=1000, items=[])
I've tried a custom KryoRegistrator to see if it was a problem with Kotlin's HashSet:
class MyRegistrator : KryoRegistrator {
override fun registerClasses(kryo: Kryo) {
kryo.register(HashSet::class.java, JavaSerializer()) // kotlin's HashSet
}
}
But it doesn't seem to help.
Any other ideas?
Full code here.
It does seem to be a serialization issue.
The documentation of Encoders.bean states (Spark v2.4.0):
collection types: only array and java.util.List currently, map support is in progress
Porting the Transaction data class to Java and changing items to a java.util.List seems to help.
I want to compare a pattern in string
sealed trait Demo { def value: String }
object Demo {
case object TypeAB extends Demo {
val value = "a:b"
}
.......other constants
}
val test = Option("a:b:c")
val s =test.map(_.startsWith(Demo.TypeAB.value))
I want to not use .value in Demo.TypeAB.value
Is there a better approach to achieve the above .I preferred to use startsWith
I tried but it didnot work
def unapply(arg: Demo): String= arg.value
sealed trait Demo {
def value: String
}
object Demo {
case object TypeAB extends Demo {
val value = "a:b"
}
implicit def demoToString(demo: Demo): String = demo.value
}
You can now write "a:b:c".startsWith(Demo.TypeAB)
Whether it's a good idea to have an implicit Demo to string method in your code, well, I'll leave it up to you :D
You could add predicates to Demo that provide the tests you need:
sealed trait Demo {
def value: String
def startsWith(body: Option[String]): Boolean = body match {
case Some(content) => content.startsWith(value)
case _ => false
}
}
This allows you to hide the implementation details at the cost of a broader interface.
Does this counts as a better way:
sealed trait Demo {
def value: String
def startsWith(s: String): Boolean = s.startsWith(value)
}
object Demo {
case object TypeAB extends Demo {
val value = "a:b"
}
}
val test = Option("a:b:c")
val s = test.map(Demo.TypeAB.startsWith(_))
println(s)
or maybe you want to use implicits magic such as
sealed trait Demo { def value: String }
implicit class DemoStringOps(val s: String) extends AnyRef {
def startsWith(d: Demo) = s.startsWith(d.value)
}
object Demo {
case object TypeAB extends Demo {
val value = "a:b"
}
}
val test = Option("a:b:c")
val s = test.map(_.startsWith(Demo.TypeAB))
println(s)
I am building a automated swagger plugin. Here I run through annotated classes.
When we talk about the datatypes of String, Long, etc. is is enough for me use the simpleName method.
But when get to a Class of List, Set, Collection I need to know the generic type.
So how can I do this?
A example of code which do most of the job:
class Foo {
List<String> myString
}
class SomeUtilClass {
static String dataType(Class<?> c) {
return c.simpleName
}
static List<String> dataTypes(Class<?> c) {
return c.metaClass.properties.findAll {MetaProperty metaProperty ->
metaProperty?.field != null
}.collect {dataType(it.type)}
}
}
SomeUtilClass.dataTypes(Foo) // ["List"] but I want something like ["List<String>"]
I found the solution. I can look on the generic type from Cached fields.
See below example:
class SomeUtilClass {
static String dataType(Class<?> c) {
return c.simpleName
}
static List<String> dataTypes(Class<?> c) {
return c.metaClass.properties.findAll {MetaProperty metaProperty ->
metaProperty?.field != null
}.collect {findGenerics(it.type)}
}
static void findGenerics(CachedField t) {
t.field.genericType?.actualTypeArguments.collect {dataType(it)}
}
}
In java we can write thead-safe singletons using double Checked Locking & volatile:
public class Singleton {
private static volatile Singleton instance;
public static Singleton getInstance(String arg) {
Singleton localInstance = instance;
if (localInstance == null) {
synchronized (Singleton.class) {
localInstance = instance;
if (localInstance == null) {
instance = localInstance = new Singleton(arg);
}
}
}
return localInstance;
}
}
How we can write it in kotlin?
About object
object A {
object B {}
object C {}
init {
C.hashCode()
}
}
I used kotlin decompiler to get that
public final class A {
public static final A INSTANCE;
private A() {
INSTANCE = (A)this;
A.C.INSTANCE.hashCode();
}
static {
new A();
}
public static final class B {
public static final A.B INSTANCE;
private B() {
INSTANCE = (A.B)this;
}
static {
new A.B();
}
}
public static final class C {
public static final A.C INSTANCE;
private C() {
INSTANCE = (A.C)this;
}
static {
new A.C();
}
}
}
All of object have constructor invoke in static block. Based on it, we can think that it's not lazy.
Сlose to the right answer.
class Singleton {
companion object {
val instance: Singleton by lazy(LazyThreadSafetyMode.PUBLICATION) { Singleton() }
}
}
Decompiled:
public static final class Companion {
// $FF: synthetic field
private static final KProperty[] $$delegatedProperties = new KProperty[]{(KProperty)Reflection.property1(new PropertyReference1Impl(Reflection.getOrCreateKotlinClass(Singleton.Companion.class), "instance", "getInstance()Lru/example/project/tech/Singleton;"))};
#NotNull
public final Singleton getInstance() {
Lazy var1 = Singleton.instance$delegate;
KProperty var3 = $$delegatedProperties[0];
return (Singleton)var1.getValue();
}
private Companion() {
}
// $FF: synthetic method
public Companion(DefaultConstructorMarker $constructor_marker) {
this();
}
}
I hope Kotlin developers will make non reflection implementation in future...
Kotlin has an equivalent of your Java code, but more safe. Your double lock check is not recommended even for Java. In Java you should use an inner class on the static which is also explained in Initialization-on-demand holder idiom.
But that's Java. In Kotlin, simply use an object (and optionally a lazy delegate):
object Singletons {
val something: OfMyType by lazy() { ... }
val somethingLazyButLessSo: OtherType = OtherType()
val moreLazies: FancyType by lazy() { ... }
}
You can then access any member variable:
// Singletons is lazy instantiated now, then something is lazy instantiated after.
val thing = Singletons.something // This is Doubly Lazy!
// this one is already loaded due to previous line
val eager = Singletons.somethingLazyButLessSo
// and Singletons.moreLazies isn't loaded yet until first access...
Kotlin intentionally avoids the confusion people have with singletons in Java. And avoids the "wrong versions" of this pattern -- of which there are many. It instead provides the simpler and the safest form of singletons.
Given the use of lazy(), if you have other members each would individually be lazy. And since they are initialized in the lambda passed to lazy() you can do things that you were asking about for about customizing the constructor, and for each member property.
As a result you have lazy loading of Singletons object (on first access of instance), and then lazier loading of something (on first access of member), and complete flexibility in object construction.
See also:
lazy() function
Lazy thread safe mode options
Object declarations
As a side note, look at object registry type libraries for Kotlin that are similar to dependency injection, giving you singletons with injection options:
Injekt - I'm the author
Kodein - Very similar and good
Object declaration is exactly for this purpose:
object Singleton {
//singleton members
}
It is lazy and thread-safe, it initializes upon first call, much as Java's static initializers.
You can declare an object at top level or inside a class or another object.
For more info about working with objects from Java, please refer to this answer.
As to the parameter, if you want to achieve exactly the same semantics (first call to getInstance takes its argument to initialize the singleton, following calls just return the instance, dropping the arguments), I would suggest this construct:
private object SingletonInit { //invisible outside the file
lateinit var arg0: String
}
object Singleton {
val arg0: String = SingletonInit.arg0
}
fun Singleton(arg0: String): Singleton { //mimic a constructor, if you want
synchronized(SingletonInit) {
SingletonInit.arg0 = arg0
return Singleton
}
}
The main flaw of this solution is that it requires the singleton to be defined in a separate file to hide the object SingletonInit, and you cannot reference Singleton directly until it's initialized.
Also, see a similar question about providing arguments to a singleton.
I recently wrote an article on that topic.
TL;DR Here's the solution I came up to:
1) Create a SingletonHolder class. You only have to write it once:
open class SingletonHolder<out T, in A>(creator: (A) -> T) {
private var creator: ((A) -> T)? = creator
#Volatile private var instance: T? = null
fun getInstance(arg: A): T {
val i = instance
if (i != null) {
return i
}
return synchronized(this) {
val i2 = instance
if (i2 != null) {
i2
} else {
val created = creator!!(arg)
instance = created
creator = null
created
}
}
}
}
2) Use it like this in your singletons:
class MySingleton private constructor(arg: ArgumentType) {
init {
// Init using argument
}
companion object : SingletonHolder<MySingleton, ArgumentType>(::MySingleton)
}
The singleton initialization will be lazy and thread-safe.