Building a simple DSL

We can now put to use what we learned about receiver and infix functions and create a DSL for validating objects. To keep it simple, we'll only be validatingInttypes.

First, we'll add the NumberValidator interface. This is where all the different validators can represent their validation logic:

interface NumberValidator 
{

fun isValueValid(value: Int): Boolean

}

Then, we need a type that will keep all the validators and the validated object. We'll name it Validator:

class Validator<T> private constructor(private val validatedObject: T) {

internal val validators = mutableListOf<NumberValidator>()
private lateinit var valueFactory: (T) -> Int
}

To enforce type safety, the Validator type is generic. It has a list of validators and also holds a function type called valueFactory, which knows how to return a property that will be validated. Notice how the constructor is private. We don’t allow the validator type to be created from outside; instead, we use an...