Kotlin - Replace class delegation - Multiple classes with same functionality different signature

Question

I am working with JunitRules RuleChain and Kotlin. I am new to both and have two classes that do the exact same thing, the only difference being the rule chain.

The first class looks like this :

class BaseActivityTestRule<T : Activity>(
    private val activityRule : ActivityRule<T>
) : TestRule by RuleChain.outerRule(CustomRuleOne).around(activityRule) {

    // do something 
}

I require another class that does the exact same thing as BaseActivityTestRule but the delegate is different.

Example :

class ExtendedActivityTestRule<T : Activity>(
    private val activityRule : ActivityRule<T>
) : TestRule by RuleChain.outerRule(CustomRuleOne).around(CustomRuleTwo).around(activityRule) {

    // do something 
}

How can I accomplish this without duplicating code blocks?

Answer 1

Just pass a boolean parameter to your constructor and use it to create the basic or extended TestRule:

fun <T> createTestRule(activityRule: ActivityRule<T>, extended: Boolean) = 
    if(extended) 
        RuleChain.outerRule(CustomRuleOne).around(CustomRuleTwo).around(activityRule)
    else
        RuleChain.outerRule(CustomRuleOne).around(activityRule)

class ActivityTestRule<T : Activity>(
    private val activityRule : ActivityRule<T>,
    extended: Boolean = false
) : TestRule by createTestRule(activityRule, extended) {

    // do something 
}