> On Jan 11, 2017, at 10:53 AM, Matthew Johnson via swift-evolution 
> <[email protected]> wrote:
> 
>> 
>> On Jan 11, 2017, at 12:32 PM, Erica Sadun via swift-evolution 
>> <[email protected] <mailto:[email protected]>> wrote:
>> 
>> 
>>> On Jan 11, 2017, at 12:26 AM, Chris Lattner via swift-evolution 
>>> <[email protected] <mailto:[email protected]>> wrote:
>>> 
>>> On Jan 10, 2017, at 11:40 AM, Douglas Gregor via swift-evolution 
>>> <[email protected] <mailto:[email protected]>> wrote:
>>>>> On Jan 10, 2017, at 10:34 AM, Michael Ilseman via swift-evolution 
>>>>> <[email protected] <mailto:[email protected]>> wrote:
>>>>> 
>>>>> [Forgot to CC swift-evolution the first time]
>>>>> 
>>>>> When this came up last, it was seen as more so a bug in the current 
>>>>> implementation, rather than an explicit choice. There's no need for a 
>>>>> proposal, just a JIRA: 
>>>>> https://bugs.swift.org/browse/SR-115?jql=text%20~%20%22Generic%20subscript%22
>>>>>  
>>>>> <https://bugs.swift.org/browse/SR-115?jql=text%20~%20%22Generic%20subscript%22>
>>>>>  
>>>> 
>>>> It’s a nontrivial new user-facing feature with new syntax in the language, 
>>>> so it’ll need a proposal. ‘twould be good for the proposal to link to the 
>>>> JIRA ticket.
>>>> 
>>>> I’ve only heard positive reactions toward this feature, and it’s something 
>>>> that the standard library could make good use of.
>>> 
>>> +1, this would be clearly great to happen.
>>> 
>>> -Chris
>> 
>> 
>> I apologize for adding to this topic rather than starting a new one, but I 
>> figure people interested in subscripts would be more likely to see my 
>> question:
>> 
>> Is there a good reason subscripts cannot throw? Right now you can create a 
>> [safe: index] subscript to return an optional but you can't create one that 
>> returns an unwrapped value or throws.
> 
> These topics do tend to come up together they are the two unnecessary 
> limitations subscripts have right now.  I hope both make it into Swift 4.  
> I’m sure we’ll see a proposal after phase 2 opens up.

Another limitation is that subscripts cannot have default arguments. I don’t 
believe this even requires an evolution proposal, it’s a quirk of the 
implementation and can be fixed by cleaning up some duplicated code paths in 
SILGen. If anyone is interested in looking at this I can point you to the code 
in question.

Slava

> 
>> 
>> Thanks, -- E
>> 
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