[swift-evolution] [Review] SE-0105: Removing Where Clauses from For-In Loops

[plx]

-1 for the reasons already brought up. 

I would also point out that half the biasing argument is extremely questionable: yes, for-in-where is “biased” in favor of “visit-if” and not "visit-unless”, but this form of “bias” is inevitable unless you start multiplying keywords (to have one for each “polarity”).

Note that, e.g., `guard` is also biased in a particular direction — we have `guard $conditionThatMustBeTrue` but not `unless $conditionThatShouldNotBeFalse` — and although this choice *does* make sense (due to let-binding being a success-case), it *is* otherwise backwards from traditional guard clauses (which were usually `if $exitCondition { $exit }`, which is the opposite polarity from how `guard` works).

So unless you want to have 2 of every control-flow keyword, whenever you have just one of each you just have to learn the “polarity" of each…this seems inevitable. Also note that even if you *did* go for 2-of-each, picking names that are sufficiently self-evident is harder than it looks, so in practice you’d almost certainly still have to wind up learning at least one of them, if not both.

Additionally, I would point `for-in-where` has some unique aspects that would complicate taking the “remove today to improve tomorrow” approach (as has been done with some other features like splatting).

Specifically, using for-in-where is a stylistic decision, and although translating its uses *to* `guard-continue` form can be done mechanically, translating `guard-continue` *back* to the (successor of) `for-in-where` in a stylistically-appropriate way seems much harder to mechanize…so if it was dropped for later, improved reinstatement, the temporary dropping might result in losing a lot of the original human stylistic choice, which IMHO is useful evidence of the original human intent.

> On Jun 22, 2016, at 11:12 PM, Chris Lattner via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Hello Swift community,
> 
> The review of "SE-0105: Removing Where Clauses from For-In Loops" begins now and runs through June 29. The proposal is available here:
> 
> 	https://github.com/apple/swift-evolution/blob/master/proposals/0105-remove-where-from-forin-loops.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
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> or, if you would like to keep your feedback private, directly to the review manager.
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> What goes into a review?
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> The goal of the review process is to improve the proposal under review through constructive criticism and contribute to 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?
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> More information about the Swift evolution process is available at
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> 	https://github.com/apple/swift-evolution/blob/master/process.md
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> 
> -Chris Lattner
> Review Manager
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