I need to write two functions to get the output format and the output index for file conversion. As part of this, I wrote a TransformSettings class for these methods and set the default value. And in the transformer class, I created a new object of TransformSettings class to get the default values for each job run. Also, I have another class called ParquetTransformer that extends Transformer where I want to change these default values. So I implemented like below.
class TransformSettings{
def getOuputFormat: String = {
"orc"
}
def getOuputIndex(table: AWSGlueDDL.Table): Option[String] = {
table.StorageDescriptor.SerdeInfo.Parameters.get("orc.column.index.access")
}
}
class Transformer{
def getTransformSettings: TransformSettings = {
new TransformSettings
}
def posttransform(table: AWSGlueDDL.Table):Dateframe ={
val indexAccess = getTransformSettings.getOuputIndex(table: AWSGlueDDL.Table)
........
}
}
class ParquetTransformer extends Transformer{
override def getTransformSettings: TransformSettings = {
val transformSettings = new TransformSettings {
override def getOuputFormat: String = {
"parquet"
}
override def getOuputIndex(table: AWSGlueDDL.Table): Option[String] = {
table.StorageDescriptor.SerdeInfo.Parameters.get("parquet.column.index.access")
}
}
}
}
Is there a way to avoid creating a brand new object of TransformSettings in Transfomer class every time this is called?
Also is there a way to rewrite the code using Scala value class?
As #Dima proposed in the comments try to make TransformSettings a field / constructor parameter (a val) in the class Transformer and instantiate them outside
class TransformSettings{
def getOuputFormat: String = {
"orc"
}
def getOuputIndex(table: AWSGlueDDL.Table): Option[String] = {
table.StorageDescriptor.SerdeInfo.Parameters.get("orc.column.index.access")
}
}
class Transformer(val transformSettings: TransformSettings) {
def posttransform(table: AWSGlueDDL.Table): DataFrame ={
val indexAccess = transformSettings.getOuputIndex(table: AWSGlueDDL.Table)
???
}
}
val parquetTransformSettings = new TransformSettings {
override def getOuputFormat: String = {
"parquet"
}
override def getOuputIndex(table: AWSGlueDDL.Table): Option[String] = {
table.StorageDescriptor.SerdeInfo.Parameters.get("parquet.column.index.access")
}
}
class ParquetTransformer extends Transformer(parquetTransformSettings)
You don't seem to need value classes (... extends AnyVal) now. They are more about unboxing, not about life-cycle management. TransformSettings and Transformer can't be value classes because they are not final (you're extending them in class ParquetTransformer extends Transformer... and new TransformSettings { ... }). By the way, value classes have many limatations
https://failex.blogspot.com/2017/04/the-high-cost-of-anyval-subclasses.html
https://github.com/scala/bug/issues/12271
Besides value classes, there are scala-newtype library in Scala 2 and opaque types in Scala 3.
Related
When I mock the particular object method is executing the actual behavior.
The expected output should be 10since I mocked the Calculate.add and returning the result as 10
trait Base {
def add (parm1:Int, parm2:Int): Int
def fetc ():Any
def compute(): Any
}
object Calculate extends Base {
def add(parm1:Int, parm2:Int):Int = {
fetc()
compute
}
def fetc ():Any = {
// Making some api1 call
}
def compute ():Any = {
// Making some api2 call
}
}
object Engine {
def execute():any{
Calculate.add(10, 20)
}
}
Test
class TestEngine extends MockFactory {
it should "compute" in {
val res1:Int = 10
val calculate: Base = stub[Base]
val data = (calculate.add _).when(10, 20).returns(res1);
Engine.execute() // ExpectedOutput should be 10(res1),Since the I mocked the add method and returning the 10 value. Should not call the Calculate object fetch, compute behaviour.
}
}
Though Calculate is mocked & add method has been stubbed, still the actual functionality of add will be executed, since in Engine.execute method Calculate object reference is used to access the add method also Calculate is itself an object, thus the actual code will be executed.
object Engine {
def execute():any{
Calculate.add(10, 20)
}
}
Simple solution to mocked calculate in Engine.execute could be instead of using Calculate object passed a base variable as method parameter.
object Engine {
def execute(base: Base): Int = {
base.add(10, 20)
}
}
class TestEngine extends MockFactory {
it should "compute" in {
val res1: Int = 10
val calculate: Base = stub[Base]
val data = (calculate.add _).when(10, 20).returns(res1);
//mocked_calculate
Engine.execute(mocked_calculate)
}
}
Assume I have the following scala classes, is it possible to extend a function on SecondClass and add more code to it? (possibly chained to another function within the function i'd like to extend)
package io.gatling.http.check
class FirstClass {
def login() = {
exec(http("Login")
.post("anonymous/login")
.body(ElFileBody("rest/UserAnonymousLogin.json")).asJson
}
}
I would like to extend the login function with the following (.check(status is 200)
class SecondClass extends FirstClass {
def login() = {
.check(status is 200))
}
}
Is that possible?
The syntax you're looking for is
class X {
def go(a: Int) = ???
}
class Y extends X {
override def go(a: Int) = {
val u = super.go(a)
// do things with `u` and return whatever
}
}
You'll need to do a little refactoring to get your code in this shape. I envisage
class FirstClass {
def body = ElFileBody("rest/UserAnonymousLogin.json")
// stuff that calls `body`
}
class SecondClass {
override def body = super.body.check(status is 200)
// no need to redefine stuff as it's inherited from `FirstClass`
}
Given checks method accepts a variable number of HttpCheck, that is, HttpCheck*
def check(checks: HttpCheck*): HttpRequestBuilder
consider refactoring FirstClass to
class FirstClass {
def login(checks: HttpCheck*) = {
exec(http("Login")
.post("anonymous/login")
.body(ElFileBody("rest/UserAnonymousLogin.json")).asJson
.check(checks: _*)
)
}
}
Note how by default we pass no checks when calling (new FirstClass).login().
Now derived classes could pass in a checks to be performed like so
class SecondClass extends FirstClass {
def loginWithStatusCheck() = {
super.login(status is 200)
}
}
Note we are not actually overriding FirstClass.login here.
Another approach instead of overriding could be functional composition, for example, we break down the problem into smaller functions
val buildClient: String => Http = http(_)
val buildPostRequest: Http => HttpRequestBuilder = _.post("anonymous/login").body(ElFileBody("rest/UserAnonymousLogin.json")).asJson
val checkStatus: HttpRequestBuilder => HttpRequestBuilder = _.check(status is 200)
and then compose them
exec((buildClient andThen buildPostRequest andThen checkStatus)("Login"))
Now we can simply add further steps to the composition instead of worrying about class hierarchies and overriding.
I have something like this:
abstract class HaveData{
val data:String
}
class HD1 extends HaveData{
val data = "HD1 data"
}
class HD2 extends HaveData{
val data = "HD2 data"
object InnerHD extends HD1{
def prt = println(data)
}
}
I want to print "HD2 data" not "HD1 data", how to do that?
I may turn InnerHD to a class and provide data as a param but is there a better way?
For this kind of situations you can use a self-type, for this specific problem, you do not need to add a different type.
abstract class HaveData {
def data: String
}
class HD1 extends HaveData {
override val data = "HD1 data"
}
class HD2 extends HaveData { self => // Alias to this in the HD2 level.
override val data = "HD2 data"
object InnerHD extends HD1 {
def prt(): Unit = {
println(self.data)
}
}
}
(new HD2).InnerHD.prt()
// HD2 data
You can also use
def prt = println(HD2.this.data)
Let's say I've got two traits, one of them being a factory for another:
trait BaseT {
val name: String
def introduceYourself() = println("Hi, I am " +name)
// some other members ...
}
trait BaseTBuilder {
def build: BaseT
}
Now, I want to extend BaseT:
trait ExtendedT extends BaseT {
val someNewCoolField: Int
override def introduceYourself() = {
super.introduceYourself()
println(someNewCoolField)
}
// some other extra fields
Let's say I know how to initialize the new fields, but I'd like to use BaseTBuilder for initializing superclass members. Is there a possibility to create a trait that would be able to instantiate ExtendedT somehow? This approach obviously fails:
trait ExtendedTBuilder { self: TBuilder =>
def build: ExtendedT = {
val base = self.build()
val extended = base.asInstanceOf[ExtendedT] // this cannot work
extended.someNewCoolField = 4 // this cannot work either, assignment to val
extended
}
def buildDifferently: ExtendedT = {
new ExtendedT(4) // this fails, we don't know anything about constructors of ExtendedT
}
def build3: ExtendedT = {
self.build() with {someNewCoolField=5} //that would be cool, but it cannot work either
}
}
I'd like to have such a set of traits (or objects) that when someone supplies concrete implementation of BaseT and BaseTBuilder I could instantiantiate ExtendedT by writing:
val extendedBuilder = new ConcreteBaseTBuilder with ExtendedTBuilder
val e: ExtendedT = extendedBuilder.build
ExtendedT could contain a field of type BaseT, but then it would require manually proxying all the necessary methods and fields, which is in my opinion a violation of DRY principle. How to solve that?
How about create ExtendBaseT instance in your ExtendBaseTBuilder
trait ExtendBaseTBuilder { self : BaseTBuilder =>
def build: ExtendBaseT = {
new ExtendBaseT {
val someNewCoolField: Int = 3
}
}
}
As far as I understand it, Scala creates an anonymous class if I create a class using the new keyword and follow the class name with a constructor:
class MyClass {
def doStuff() {
// ...
}
}
val mc = new MyClass {
doStuff()
}
The nice thing being that all the code in the constructor is in the scope of the new object.
Is there a way I can reproduce this syntax where the class is created by a factory method rather than the new keyword? i.e. make the following code work:
val mf = new MyFactory
val mc = mf.MyClass {
doStuff()
}
I can't find a way to do it but Scala has so much to it that this might be pretty easy!
Using an import as suggested by #Ricky below I can get:
val mf = MyFactory;
val mc = mf.MyClass
{
import mc._
doStuff()
}
(Where the blank line before the block is needed) but that code block is not a constructor.
You can do this, but you still have to keep the new keyword, and create the nested class as a path-dependent type:
class Bippy(x: Int) {
class Bop {
def getIt = x
}
}
val bip = new Bippy(7)
val bop = new bip.Bop
bop.getIt // yields 7
val bop2 = new bip.Bop{ override def getIt = 42 }
bop2.getIt // yields 42
I don't think it's possible. However, a common pattern is to add a parameter to factory methods which takes a function modifying the created object:
trait MyClass {
var name = ""
def doStuff():Unit
}
class Foo extends MyClass {
def doStuff() { println("FOO: " + name) }
}
trait MyClassFactory {
def make: MyClass
def apply( body: MyClass => Unit ) = {
val mc = make
body(mc)
mc
}
}
object FooFactory extends MyClassFactory {
def make = new Foo
}
You can then create and modify instance with a syntax close to your example:
val foo = FooFactory { f=>
f.name = "Joe"
f.doStuff
}
It sounds like you're just looking to mix in a trait. Instead of calling myFactoryMethod(classOf[Foo]] which ideally would do (if Scala permitted it):
new T {
override def toString = "My implementation here."
}
you can instead write
trait MyImplementation {
override def toString = "My implementation here."
}
new Foo with MyImplementation
However, if you are just looking to get the members of the new object accessible without qualification, remember you can import from any stable identifier:
val foo = new Bar
import foo._
println(baz) //where baz is a member of foo.