[swift-evolution] [Review] SE-0018 Flexible Memberwise Initialization

Stephen Christopher schristopher at bignerdranch.com
Sun Jan 10 15:47:56 CST 2016

> The review of "Flexible Memberwise Initialization" begins now and runs
> through January 10th. The proposal is available here:
> https://github.com/apple/swift-evolution/blob/master/proposals/0018-flexible-memberwise-initialization.md


>         * What is your evaluation of the proposal?
 A slightly hesitant +1. I think there may be a more general approach that
would have benefits across the language, although that approach would still
need several specific accommodations to work for init. I’m not sure a
comparable solution would land anywhere better in the complexity space,
though it could probably provide a less narrow set of advantages.

        * Is the problem being addressed significant enough to warrant a
> change to Swift?
 Yes. Initialization is fundamental to Swift, and as it stands right now
there is too much boilerplate. I believe this proposal carefully worked
through the space of attempting to minimize need for boilerplate in enough
common cases without requiring too much special knowledge.

        * Does this proposal fit well with the feel and direction of Swift?
I think so, overall. It strikes a pretty good balance. I am reluctant to
make teaching initialization any more difficult, but I looked through the
proposal yet again with an eye towards how I would teach this new feature
along with everything else and I believe it is manageable (and in fact not
as high a cost as I assumed previously). I don’t think most of the future
possible directions will be needed or beneficial, but the proposal as it
stands today does not complicate the language overly much from my
perspective, relative to its benefits. I do wish some of the ideas on a
more general solution had come up earlier and had time to be more fully
explored. Using a broader feature with specialization for init would be the
best possible improvement  in fitting with Swift that I could imagine.

In the end I think this is a good and very well thought through proposal on
memberwise initialization. I think it strikes a very good balance on
capability vs additional complexity, with the caveat that I think it is a
bit too narrow and we should have explored a more general variadic args
capability to underly this feature earlier. However I’m not sure we should
hold up this proposal based on that hypothetical, especially since much of
the initialization-specific capabilities would still need to be addressed.

>         * If you have you used other languages or libraries with a similar
> feature, how do you feel that this proposal compares to those?
Nothing comes to mind that would be comparable.

        * How much effort did you put into your review? A glance, a quick
> reading, or an in-depth study?
I’ve followed the entire discussion(s) on Swift-Evolution, and read the
proposal several times. I went through some of our Swift codebase, and
thought through the impact on our Initialization lecture and materials.

- Step
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