ContextPlayground.kt

// It seems that a Delegate Class always forwards to the same instance that it was created with. 
// But it opens a possible misunderstanding: If I declare the delegated instance in the constructor 
// as a var, shouldn't it change behaviour when the var changes? Or shouldn't a delegated instance 
// always be a val, so it can't be changed? I think I prefer the first, as it would give the user more choice.

// General Interface
interface Context {
    fun print(printable: String)
}

// Basic Implementation of Context, just prints to console the same data
class BasicContext : Context {
    override fun print(printable: String) {
        System.out.println(printable)
    }
}

// Basic Implementation of Context, just prints to console with quotes
class QuotedContext : Context {
    override fun print(printable: String) {
        System.out.println("\"$printable\"")
    }
}

// Delegated Context, doesn't change context on call
class DelegatedContextWrapper(private var context: Context = BasicContext()) : Context by context {
    fun changeContext(context: Context) {
        this.context = context
    }
}

fun main(args: Array<String>) {
    val printable = "It's Alive!"
    val context = DelegatedContextWrapper()

    // Print the same way
    context.print(printable)

    // Changes to Quotable Context
    context.changeContext(QuotedContext())

    // Should print in quotes, isn't
    context.print(printable)
}