[swift-evolution] [Review] SE-0005 Better Translation of Objective-C APIs Into Swift

Drew Crawford drew at sealedabstract.com
Mon Feb 1 15:38:09 CST 2016

> On Feb 1, 2016, at 1:02 PM, Tony Parker <anthony.parker at apple.com> wrote:
> Types like NSURL are intended to be the canonical URL for everyone to use,

I think the "canonical URL for everyone to use" must be a value type / struct.  To me this seems axiomatic.

Meanwhile (NS)URL cannot be a value type because of the Darwin compatibility mandate, and to change from value->reference semantics would be "off the charts" breakage severity.

This is a requirements conflict.  corelibs-foundation can either be Darwin-compatible or it can be canonical, but we cannot do both.  Right now we have chosen Darwin-compatible, so we must let the canonical requirement go.   Unprefixed "URL" should be reserved for the value type that can actually work as a canonical API.

It's not clear to me if Foundation will actually be in a position to provide that API (e.g. in Swift 4, etc.) or whether some third party will provide a "URL" framework that gains traction first.  But in any case, we are not going to do it in the Swift 3 window, unless a lot of core scope decisions get re-decided.

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