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

Brent Royal-Gordon brent at architechies.com
Sat Feb 18 05:49:24 CST 2017

> On Feb 17, 2017, at 7:26 PM, John McCall <rjmccall at apple.com> wrote:
> 	Proposal link: https://github.com/apple/swift-evolution/blob/master/proposals/0155-normalize-enum-case-representation.md
> 	• What is your evaluation of the proposal?

I'm torn. Being able to handle the associated value as a tuple is very convenient, but I also want the argument list features described here. In practice, my own enums tend to end up using argument-like parameter labels, which works better when constructing and pattern-matching, but worse when extracting values.

I think I'd like to ask for two changes. One is probably easy; the other is a bit of a stretch.

Easy: Cases should allow internal names for documentation and autocompletion.

	enum SQLError: Error {
		case valueInvalid(_ underlying: Error, for key: SQLColumnKey, in statement: SQLStatement)
	throw SQLError.valueInvalid(error, for: key, in: statement)
	switch sqlError {
	case let .valueInvalid(<#underlying#>, for: <#key#>, in: <#statement#>):

Stretch: There should be a way to extract the associated values during a pattern match as a tuple. Sketch (with strawman syntax):

	// Different forms of the same case statement:
	case let .valueInvalid(underlying, for: key, in: statement):
	case let params in . valueInvalid:

	case let params in . valueInvalid(_:for:in:):

	case let (underlying, key, statement) in . valueInvalid:

	case let (underlying, key, statement) in . valueInvalid(_:for:in:):

Other than these things, I'm pretty happy with this proposal. I agree with the ideas of treating the labels as part of the case name, making them more usable as functions, and supporting default values.

> 	• Is the problem being addressed significant enough to warrant a change to Swift?

Yes—the issues described in the "Motivation" section are pretty ugly.

> 	• 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?

Not really in-depth, but I did put some thought into it.

Brent Royal-Gordon

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