I just don't understand the difference or why one of them fails.

You’re simply not initializing

master

before

data

But it crashes on access to

hash

, not during construction - or am I way out here? Note that this is an

abstract

and there

is

a

master

at that time is there not? So what is the difference and why does changing

data

make

hash

work?

Yes!

master

is

null

when I request the

hash

and that is long after the actual object has finished construction.

object FooImageData : ImageData() {
    override val master = listOf(
        "424d3684030000000000..."
        // ...
    )
}

Well that’s just not possible so I’m gonna keep saying your object hasn’t finished construction yet the first time you call

hash

Well that’s just not possible

My feelings exactly! Which is why I chose to ask here. 🙂