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

Daniel Duan daniel at duan.org
Sun Feb 19 11:56:14 CST 2017

Hi Dave,

> On Feb 18, 2017, at 8:49 PM, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
> I'm on vacation and don't have time for a full review right now, but I am concerned that wild this proposal would make enums more general and uniform with the rest of the language , they also would become much more awkward for common use cases. I have recently been very pleased that I didn't have to supply labels in switch statements where the label name would simply have matched the name of the variable to be bound.  This looks needlessly verbose:
>   case .valid(value: let value, resumptionPoint: let resumptionPoint):
> I cannot imagine a real life use case where one would have labels in the case and desire to bind associated values to variables having different names than the labels

The degraded authoring experience is a legitimate concern. Here’s my attempt to make it *seems* better:

1. Perhaps it’d be a good style to treat labels similar to argument labels and variables in patterns as argument names:

    case let .value(validated: value, resumingAt: point) // or more descriptive variable names, depends on usage

We’ve came to expect some repetition between a argument label and its name, so typing a few more characters for the label in patterns shouldn’t seem totally bad, maybe. From a code reader's point of view, especially for those who haven’t seen the case declaration, more labels should be an easy win.

2. The creator of the enum dictates style at use site. When one prefers no not have labels, they can use comments as documentation at the declaration.


That being said, the idea of matching without field name appeals to me because I’m used to it from other languages.

> Secondly, I can't imagine a case where one would want to use the same case basename and different labels. The very common use case where the types of associated values completely distinguish the case and one would rather not have to supply a case name at all is completely unaddressed. If my quick read is not mistaken, this proposal makes it legal for cases to have different complete names (including base name and labels), but doesn't make it legal to have the same full name (which I would love to be "_" or missing in some cases) with different associated value types. If we were truly following the precedent set by function signatures, wouldn't that be possible too?

Love it. I think this should be part of this proposal. (man, if you squint, those cases named “_" make the whole declaration look like a C union).

> Sent from my moss-covered three-handled family gradunza
> On Feb 17, 2017, at 5:26 PM, John McCall <rjmccall at apple.com <mailto:rjmccall at apple.com>> 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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