[swift-evolution] Proposal: Introduce User-defined "Dynamic Member Lookup" Types

[Joe DeCapo]

> On Dec 4, 2017, at 9:30 PM, Chris Lattner <clattner at nondot.org <mailto:clattner at nondot.org>> wrote:
> 
> I personally am far more interested in getting to the bottom of Doug’s concerns - it isn’t clear to me what exactly his preferred direction actually is, but that discussion is based on engineering tradeoffs and may well lead to a change to the proposal or a complete change in direction.
> 
> -Chris

Some notes on one of Doug's points:

> * Indexing/jump-to-definition/lookup documentation/generated interface won’t ever work. None of the IDE features supported by SourceKit will work, which will be a significant regression for users coming from a Python-capable IDE.

Here's the state of the art in PyCharm in a personal Python project (no type hints, but full comprehensive doc comments):

https://www.dropbox.com/s/ob54qalshf6gqth/Screenshot%202017-12-04%2022.11.22.png?dl=0 <https://www.dropbox.com/s/ob54qalshf6gqth/Screenshot%202017-12-04%2022.11.22.png?dl=0>

https://www.dropbox.com/s/drw6991u512g456/Screenshot%202017-12-04%2022.11.47.png?dl=0 <https://www.dropbox.com/s/drw6991u512g456/Screenshot%202017-12-04%2022.11.47.png?dl=0>

https://www.dropbox.com/s/h8wuy91r1hfnsvj/Screenshot%202017-12-04%2022.12.05.png?dl=0 <https://www.dropbox.com/s/h8wuy91r1hfnsvj/Screenshot%202017-12-04%2022.12.05.png?dl=0>

PyCharm is able to get the trivial cases right, but any of the more complex cases tend to end up looking something like that. I don't see any way that Swift could improve on that, and it's still a foreign experience to anyone used to developing Swift code in Xcode.
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