On Dec 10, 2017, at 12:22 PM, Xiaodi Wu via swift-evolution <swift-evolution@swift.org> wrote: > The last time I said this, I pointed out that this was a protocol which: > > 1. Has no formal members, > 2. But imposes informal requirements enforced by the compiler, > 3. Permits and uses arbitrary overloads, and > 4. Cannot be usefully used in a generic context or as a type constraint, > > None of which are true of ordinary protocols. Since then, we have added: > > 5. Can only be conformed to in the main declaration. > > This is looking less like a protocol by the day. The square-peg grooves in > the round hole are getting deeper and more splintery with every revision. > > Synthesized conformances cannot be declared in extensions either. If you'd > like, you could consider that this protocol is one for which the compiler > synthesizes an infinite number of members. > > I would like to see (4) addressed: a complete implementation should allow me > to call any member on a type T in a generic context where T : > DynamicMemberLookupProtocol, which I kind of assumed that this proposal would > eventually permit.
The technical problem with this is that there are no witnesses in the protocol witness table - either for the subscripts or for the conceptual associated types of the index and return value of the subscript. -Chris
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