Scala: reconfigure trait using CLI parameters

0
votes

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?

2
scala
Could you add a simplified example of what you want to achieve? The question is open for many interpretations as-is and will prompt closure as 'too broad'. See also: stackoverflow.com/help/mcve - maasg
If it really is only for testing then scalatest with Mockito could help you. - totoro

2 Answers

2
votes

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()
}
0
votes

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()