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

[Letanyan Arumugam]

> On 07 Dec 2017, at 17:02, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
> 
> 
> On Thu, Dec 7, 2017 at 00:37 Letanyan Arumugam via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
>> This seems marginally tolerable, but excessive.
>> 
>> Do we mark every usage of a type that can generate precondition failures or fatal errors for reasons other than “no such method?” No, we don’t.
>> 
> 
> fatalError shouldn’t be used excessively. API surface areas for these types are going to be massive (infinite technically). I assume many people are going to be writing a lot of code would these types and calling many methods and properties which would all essentially have a fatalError. Would you consider it good code if the majority of all your types had methods defined with fatalError calls.
> 
> What is the basis for this claim? Probably the majority of standard library methods check preconditions and trap on failure. That is how I write my code as well.
> 

I’m talking specifically about fatalError not precondition. fatalError is something that goes out with production code while precondition is used for debugging. I think you would agree a shipped program that has many states of being unrecoverable is not a good design?
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