[swift-evolution] [Pitch] Limit Implicit Capture

Jordan Rose jordan_rose at apple.com
Wed Mar 16 13:24:18 CDT 2016

> On Mar 16, 2016, at 11:11, Joe Groff <jgroff at apple.com> wrote:
>> On Mar 16, 2016, at 11:09 AM, Jordan Rose via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> It's worth noting that—for better or for worse—explicit capture has different semantics from implicit capture today. If a local variable ('var', not 'let') is captured, it is captured by value when mentioned explicitly and by reference when not. This is discussed in The Swift Programming Language <https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/doc/uid/TP40014097-CH32-ID544>.
>> If you were to then propose a syntax of `inout x` or `&x`, I would argue that there is no inout-ish behavior: updates to the variable both inside and outside the closure (a) are always reflected immediately (i.e. there is no writeback), and (b) are not subject to the aliasing restrictions that 'inout' has. 
>> (Not that I have an alternative spelling handy.)
> `[var x]` seems to me like a reasonable spelling for explicit `var` capture.

I forgot to preempt that one too. :-) That would be somewhat at odds with the "var x" we left in switches, which is definitely an independent variable. (Especially if someone extends it to "var x = y".)


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