Optional require(s) NonNull

[Alessio Stalla]

On Tue, Oct 30, 2012 at 2:16 PM, Roland Tepp <luolong at gmail.com> wrote:
> Hi,
>
> I was wondering, what is the rationale in implementing the Optional this
> particular way?
> (there is a thread on Java posse google group where various deficiencies of
> current implementation are discussed at some length:
> https://groups.google.com/forum/#!topic/javaposse/fTDnkfeSHsY)
>
> I myself would like to ask why have you not implemented it same way as most
> implementations of Optional I've seen have done it, by having two separate
> classes for Absent and Present values
> (I attached my take on the Optional implementation to this email).
>
> This addresses imho very nicely the usual conceptual difference between
> values that are present and those that are not.
> Only present values have get method, so there is no way to accidentally get
> from an absent value.

In Java there isn't any pattern matching construct, so such a design
would force users to write ugly code with instanceof's and type casts.

Alessio
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