[swift-evolution] [Review] SE-0155: Normalize Enum Case Representation

Daniel Duan daniel at duan.org
Sat Feb 18 14:28:49 CST 2017

Hi Slava,

> On Feb 18, 2017, at 12:30 AM, Slava Pestov via swift-evolution <swift-evolution at swift.org> wrote:
> +1, two small questions:
> - If two cases have the same base name but different full names, will matching on the base name match both cases, or will it be an error?

An error.

> - What are the memory layout optimizations described here? From a first glance this looks purely syntactic.

Nothing has stopped us from optimizing the layout further by stop using a tuple. In that sense this proposal is purely syntactic indeed. I got this idea from Joe. So I’ll just quote him here :P

“...makes it easier to allow layout optimization, since the layout of each payload would be unique to the enum instead of having to play double duty as a tuple. Since tuples are structural types and can be dynamically passed into generic contexts we're constrained by the limitations of value witness tables in laying them out; no overlapping spare bits or anything like that."

> Slava
>> On Feb 17, 2017, at 7:26 PM, John McCall via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> Hello Swift community,
>> The review of "SE-0155: Normalize Enum Case Representation" begins now and runs through next Friday, February 26th. The proposal is available here:
>> 	https://github.com/apple/swift-evolution/blob/master/proposals/0155-normalize-enum-case-representation.md <https://github.com/apple/swift-evolution/blob/master/proposals/0155-normalize-enum-case-representation.md>
>> Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at
>> 	https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>> or, if you would like to keep your feedback private, directly to the review manager. When replying, please try to keep the proposal link at the top of the message:
>> 	Proposal link: https://github.com/apple/swift-evolution/blob/master/proposals/0155-normalize-enum-case-representation.md <https://github.com/apple/swift-evolution/blob/master/proposals/0155-normalize-enum-case-representation.md>
>> 	Reply text
>> 	Other replies
>> What goes into a review?
>> The goal of the review process is to improve the proposal under review through constructive criticism and, eventually, determine the direction of Swift. When writing your review, here are some questions you might want to answer in your review:
>> 	• What is your evaluation of the proposal?
>> 	• Is the problem being addressed significant enough to warrant a change to Swift?
>> 	• Does this proposal fit well with the feel and direction of Swift?
>> 	• If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
>> 	• How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
>> More information about the Swift evolution process is available at https://github.com/apple/swift-evolution/blob/master/process.md <https://github.com/apple/swift-evolution/blob/master/process.md>
>> Thank you,
>> John McCall
>> Review Manager
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