>
>
> > A Nullable is immutable, its value isn't down the back of the couch
> > (which is my understanding of epistemological missingness, usually
> > applied to the TV remote :), it can never get a value once its null.
> That's not a technical question (immutable/mutable), but a conceptual
> one. If you have missing values in e.g. survey data, it usually means
> that the individual has not replied to the question (away, refused to
> reply, bug in the collect...). So you cannot say whether the value would
> have been 3 or something else.
>
>
In this application "no answer" is a value, not an absence of value. It is
an annoying value since it is a different type from 3 being a number, but
it is an answer nonetheless. The NA/None objects provided in other
languages (and as I understand were previously provided in Julia) are
intended to represent that value and to propagate.
Given that both viewpoints are different but valid, perhaps what has been
learnt is that Julia needs both the Null object for representing
application out-of-band values for statistics and Nullable{T} for the
computer science concept of "no value".
Or just leave (==){T}(Nullable{T}, T) undefined as it is now, so the user
can define it as they require.
Cheers
Lex
>
> Regards
>
>
