[swift-evolution] [Pitch #2] Introduce User-defined "Dynamic Member Lookup" Types

[Chris Lattner]

> On Dec 2, 2017, at 7:58 PM, Jose Cheyo Jimenez <cheyo at masters3d.com> wrote:
> 
> Hi Chis, 
> 
> Thank you for pushing this forward.
> 
> My only comment is that on the declaration side it would be great to also have an attribute to communicate that compiler magic is happening.
> 
> Currently it is surprising that a regular looking protocol is providing me so much power.
> 
> Suggestions: 
> 
> @dynamic
> struct PyVal : MemberLookupProtocol {...}
> 
> @dynamic
> struct ParameterSummer : DynamicCallable {...}
> 
> // Error: This type needs the @dynamic attribute.
> class ParamWinter : MyCustomCallableProtocolOrClassOrTypeAlias {...}
> 
> By requiring @dynamic (Or other attribute name), people can know that this is a compiler dynamic declaration and not just some random protocol whose name starts with Dynamic*. :)

I’m not a huge fan of this (because it is redundant as Jean-Daniel mentions downthread), but it is definitely possible.  I’ll add it to the alternatives section so that people consider it during review.

-Chris


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