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

[Jean-Daniel]

> …

> Beyond that, it is counterproductive to your goals, because it means that people are far less likely to use to use optional returns.  Doing so (which produces a safer result) would cause a double tax in syntax, and would be a confusing jumble.  I can’t bring myself to do the whole example above, one line - just converting member lookup syntax but not callable syntax - would end up:
> 
> 	let y =  np^.arange?^(24)^.reshape^?(2, 3, 4)
> 
> If you made DynamicCallable also return optional it would be:
> 
> 	let y =  np^.arange?^(24)?^.reshape^?(2, 3, 4)!
> 
> or something.  This is such madness that no one would do that.

Optional is not the only swift error handling pattern. But I agree that making the dynamic fonction throw would also induce a readable cost due to the necessity to add try at each call site.


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