[swift-evolution] Generic Subscripts

[Douglas Gregor]

> On Jan 11, 2017, at 10:32 AM, Erica Sadun <erica at ericasadun.com> wrote:
> 
> 
>> On Jan 11, 2017, at 12:26 AM, Chris Lattner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> On Jan 10, 2017, at 11:40 AM, Douglas Gregor via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>> On Jan 10, 2017, at 10:34 AM, Michael Ilseman via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> 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.

Throwing subscripts (and properties) do seem to fit well into the language model. There’s a well-written proposal draft by Brent here:

	https://github.com/brentdax/swift-evolution/blob/throwing-properties/proposals/0000-throwing-properties.md <https://github.com/brentdax/swift-evolution/blob/throwing-properties/proposals/0000-throwing-properties.md>

	- Doug


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