In a when block I have a lot of code like that:

"-" -> if (aggregate is Minus) Minus(*aggregate.expressions, nextExpression) else Minus(aggregate, nextExpression)
                        "+" -> if (aggregate is Plus) Plus(*aggregate.expressions, nextExpression) else Plus(aggregate, nextExpression)
....

I wanted to make that easier, but i am failing. My Idea was something like this:

private inline fun <reified T> myIdea(aggregate: InfixExpression, nextExpression: Expression): T = if (aggregate is T) 
            T(*aggregate.expressions, nextExpression)
        else
            T(aggregate, nextExpression)

using the Type T as a Constructor does not work. Any advice?

make a static 'of' function that implies T.of(...) -> T on an class parent of both Minus and Plus or use invoke constructors using reflection

As the compiler does not know which type

T

will be, it cannot know which constructors would exist, so I don't think this is possible directly. You need to resort to reflection. Use

T::class.constructors

or

T::class.java.getConstructor(type1, type2)

to find the constructor you want to invoke and then call it.

btiasD!