I have a Scala application, where pretty much every object extends a specific trait, which holds all the main functions and variables used by pretty much the entire system.
I want to add a --testing flag to my app's command line variables, which will shift the the results of some of the functions in the trait.
Putting it simply, I'd like the variable accepted in the main to have an affect that alters something in the trait before it is extended by the objects - without sending it explicitly to all objects.
Any ideas how that can be performed?
I doubt you really want to dynamically modify a trait, and I am not sure if it possible that all your classes inheriting that trait would be affected. I don't know enough about the compiler and byte code.
A way to accomplish something similar would be to have your trait take a parameter, and make your trait act conditionally on the parameter.
trait Foo {
val testing: Boolean
def fn1(): Unit = {
if (testing) {
println("testing")
} else {
println("production")
}
}
}
class Bar(val testing: Boolean) extends Foo {
def fn2(): Unit = {
fn1()
}
}
new Bar(true).fn2()
new Bar(false).fn2()
Your question is broad and this is just my 5 cents.
Update
trait Foo {
def fn1(): Unit = {
if (Foo.testing) {
println("testing")
} else {
println("production")
}
}
}
object Foo {
var testing: Boolean = false
}
class Bar extends Foo {
def fn2(): Unit = {
fn1()
}
}
object SOApp extends App {
new Bar().fn2()
Foo.testing = true
new Bar().fn2()
}
Consider passing the 'testing' flag to the trait's initializer block like this:
trait MyTrait {
var testMode: Boolean = _
def doSomething(): Unit = {
if (testMode)
println("In Test Mode")
else
println("In Standard Mode")
}
}
// IMPORTANT: Your best bet would be to create some Config object
// that is loaded and initialized in a main method.
// Define test-specific Config class:
case class Config(testMode: Boolean) {
def isTestMode: Boolean = this.testMode
}
// Instantiate in main method:
val config = new Config(true)
// Later, extend the trait:
class MyObj extends MyTrait { testMode = config.isTestMode() }
// Then just invoke
new MyObject().doSomething()
Related
I have a few functions within a scala object. The functions internally call other functions of the same object.
object A {
def method1:Unit= {
spark=CreateSparkSession.create()
Method2(spark,dbnm)
}
def Method2(spark:Sparksession, dbnm:String):Unit= {
//some implementation
}
}
How can I write Unit testcase for Method1 without actually invoking method2.
CreateSparksession is another object with create method that returns sparksession.
You cannot mock methods in an object. And you should not mock methods in class that you are testing (if it looks like you need to, it is a definite symptom of violating the single responsibility principle).
What you can do is something like this:
trait Api1 {
def method1(
...
): Unit // NB: also, should not really return a Unit: how are you going to test this???
}
trait Api2 {
def method2(...): Unit // See above
}
class Impl2 extends Api2 {
def method2(...) = // Do stuff
}
class Impl1(val api2: Api2) extends Api1 {
def method1(...) = { ... ; api2.method2(); ... }
}
// You should not really need this, but, you can have it if you want
object A extends Impl1(new Impl2)
So, now testing this code is trivial:
describe("Impl2") {
it ("does nothing") {
new Impl2().method2("foo")
// Nothing happens
// this is what I meant: how do you know it worked?
}
}
describe("Impl1") {
it ("does nothinig") {
val a2 = mock[Api2]
doNothing when a2 method2(any)
val fixture = new Impl1(a2)
fixture.method1()
// Again, nothing happens!
verify(a2).nothing("foo")
}
I am relatively new to scala so please bear me if I asked silly questions.
I have a requirement where I need to invoke a method run time.
I have a trait which is being extended by two classes
trait Animal {
def walk():DataFrame
}
This is extended by two classes.
class Dog(sparkSession: SparkSession) extends Animal {
def walk():DataFrame = {
.............
}
}
class Cat(sparkSession: SparkSession) extends Animal {
def walk():DataFrame = {
.............
}
}
Now from a config file I will get a list of these class names
Lets say like this
val animals = ["com.xy.Dog","com.xy.Cat"]
I need to invoke these classes and execute walk methods.
Can I do something like this?
animals.forEach{ animalString =>
val animalObject = Class.forName(animalString ).newInstance().asInstanceOf(Animal)
animalObject.walk
}
There are a few issues, let's take them one by one:
To build a list in scala you need to do:
val animals = List("com.xy.Dog", "com.xy.Cat")
The forEach method is actually foreach, so there's a small typo. Finally, when you call the newInstance you should get the appropriate constructor before that, otherwise it will use the default one.
animals.foreach { animalString =>
val animalObject = Class.forName(animalString)
.getConstructor(classOf[DataFrame]) // Get the constructor for a DataFrame argument
.newInstance(dataframe) // Pass the dataframe instance
.asInstanceOf[Animal]
animalObject.walk
}
I've made a couple of small changes to the code for you to see it working. You can run the app to see the output:
class Dog extends Animal {
def walk(): Unit = { println("I'm a dog.") }
}
class Cat extends Animal {
def walk(): Unit = { println("I'm a cat.") }
}
object AnimalTest extends App {
val animals = List("com.xy.Dog", "com.xy.Cat")
animals.foreach { animalString =>
val animalObject = Class.forName(animalString)
.newInstance()
.asInstanceOf[Animal]
animalObject.walk
}
}
Note that I've removed the constructor arguments here to easily build instances. The rest is about the same. I hope this helps you.
I have the following class setup:
class MyClass {
class MyInnerClass(memberVar: String)
def getAInner: MyInnerClass = {
new MyInnerClass("hello")
}
}
Then I have the following code outside of the class:
def myFunction = {
val a = new MyClass
val b = a.getAInner.memberVar // value memberVar is not a member of a.MyInnerClass
}
Why is this?
You need to add the keyword val to make memberVar public otherwise it's a private value:
class MyClass {
class MyInnerClass(val memberVar: String)
def getAInner: MyInnerClass = {
new MyInnerClass("hello")
}
}
#Noah's answer is totally correct, but I would also throw out the option of using case class. See here for some of the sugar it provides. I use it almost reflexively. In your example, it would be:
object MyClass {
case class MyInnerClass(memberVar: String)
def getAInner: MyInnerClass = {
new MyInnerClass("hello")
}
}
def myFunction = {
val b = MyClass.getAInner.memberVar
}
I tend to do it this way because invariably, I want to take advantage of the sane defaults case class provides.
I also chose to use object for the outer type, because it doesn't have any parameters, although you may have just done that for simplicity's sake.
I'm new to the Play framework and scala and I'm trying to inject a dependency inside a companion object.
I have a simple case class, like:
case class Bar(foo: Int) {}
With a companion object like:
object Bar {
val myDependency =
if (isTest) {
// Mock
}
else
{
// Actual implementation
}
val form = Form(mapping(
"foo" -> number(0, 100).verifying(foo => myDependency.validate(foo)),
)(Bar.apply)(Bar.unapply))
}
This works fine, but it's not really a clean way to do it. I'd like to be able to inject the dependency at build time so that I can inject different mock objects when testing and different real implementations in development and production.
What's the best way to achieve this?
Any help really appreciated. Thanks!
Along the lines of the Cake, we can try to change your example to
trait Validator {
def validate(foo: Int): Boolean
}
trait TestValidation {
val validator = new Validator {
def validate(foo: Int): Boolean = ...
}
}
trait ImplValidation {
val validator = new Validator {
def validate(foo: Int): Boolean = ...
}
}
trait BarBehavior {
def validator: Validator
val form = Form(mapping(...))(Bar.apply)(Bar.unapply)
}
//use this in your tests
object TestBar extends BarBehavior with TestValidation
//use this in production
object ImplBar extends BarBehavior with ImplValidation
You should additionally try and test if this example fits well within the Play Framework, too
I have the following class in my mind:
abstract class MyClass (data: MyData) {
def update(): MyClass = {
new MyClass(process())
}
def process(): MyData = {
...
}
}
However, abstract classes cannot be instantiated so the line new MyClass(process()) is an error. My question is - is there any way to tell the compiler that in case of each of the child classes of MyClass I want to create an object of exactly that child class? It seems an overkill to write this method awhole in all child classes. Playing with type parameters of the class or method I could not acheive that myself.
How about something like this? MyClass is parametrized with the concrete type. Of course, all concrete classes have to implement a method that actually returns a new instance of Self.
trait MyClass[+Self <: MyClass[Self]] {
def update(): Self = {
makeNew(process())
}
def process(): MyData = {
// ...
}
protected def makeNew(data: MyData): Self
}
class Concrete0 extends MyClass[Concrete0] {
protected def makeNew(data: MyData) = new Concrete0
}
class RefinedConcrete0 extends Concrete0 with MyClass[RefinedConcrete0] {
override protected def makeNew(data: MyData) = new RefinedConcrete0
}
Credit: IttayD’s second update to his answer to this question.
To completly avoid implementing almost identical method in all subclasses you would need to use reflection. I guess that would be your last resort if you have chosen Scala.
So here is how to minimize the repetitive code:
// additional parameter: a factory function
abstract class MyClass(data: MyData, makeNew: MyData => MyClass) {
def update(): MyClass = {
makeNew(process())
}
def process(): MyData = {
...
}
}
class Concrete(data: MyData) extends MyClass(data, new Concrete(_))
This way you repeat only the shortest fragment required to instantiate the subclass.