[swift-evolution] [Pitch] Replace the ternary operator with an in-language function

[Chris Lattner]

> On Oct 25, 2016, at 10:30 PM, Charlotte Angela Tortorella via swift-evolution <swift-evolution at swift.org> wrote:
> 
>>  Not a replacement for the Swift 4 source stability goal.
> 
> Swift 4 doesn't actually have a source stability goal. It has an ABI stability goal. These are two very different things. ABI is the calling conventions of the language.

Hi Charlotte,

Swift 4 has a strong source level compatibility goal.  This is explained in the main swift-evolution page and also in the proposal template:
https://github.com/apple/swift-evolution/blob/master/0000-template.md <https://github.com/apple/swift-evolution/blob/master/0000-template.md>

"Relative to the Swift 3 evolution process, the source compatibility requirements for Swift 4 are much more stringent: we should only break source compatibility if the Swift 3 constructs were actively harmful in some way, the volume of affected Swift 3 code is relatively small, and we can provide source compatibility (in Swift 3 compatibility mode) and migration.”

I agree with you that a migrator could handle this change, but such a significant source breaking change still needs major justification for doing so.  Further in the Swift 3 timeframe, this very topic was hotly debated by the folks who wanted to turn the if statement into an expression (eliminating the need for the ?: operator).

-Chris
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