[swift-evolution] Move placement of 'throws' statement

[Xiaodi Wu]

On Mon, Dec 26, 2016 at 2:20 PM, Tony Allevato via swift-evolution <
swift-evolution at swift.org> wrote:

> "throws" makes more sense closer to the end of the function signature
> because it's an outcome like the return type. Swift's function syntax is
> fairly consistent in this regard: <modifiers> func <name>(<inputs>)
> <outcomes>.
>
> Personally, I think the keyword is fine where it is and this is the kind
> of change where there would have to be *significant* advantages to changing
> it. I think it would be hard to make the case that a change at this point
> would warrant breaking existing code.


In a vacuum, I too would probably lean towards `throws` being closer to the
end of the signature than it is now, but that's kind of beside the point.

As a meta-comment, although this syntax was introduced prior to the
evolution process, one must expect that the core team debated between all
obvious options and chose the current one over the alternatives. Even
before the current point where source-breaking changes need "extreme"
justification, it would have required significant motivation consisting of,
say, empirical evidence of frequently incorrect code, etc., to justify a
change. The bar for revisiting previous decisions is and justifiably should
be very high; in the recent past, it's generally taken place due to glaring
difficulties found during implementation that could not be fixed without
amending a previous proposal.


On Mon, Dec 26, 2016 at 10:59 AM Lucas Neiva via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> I like "throwing" as a prefix. It's reads well and fits very nicely with
>> "mutating".
>>
>> Remembering where to put the keyword for is also easier if it's at the
>> beginning, where it fits grammatically as "throwing func".
>>
>> On 26 Dec 2016, at 19:53, Micah Hainline via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> I'd prefer the placement at the very end, I do think it would improve
>> readability, especially when taking closures as parameters and returning
>> closures. However, I don't think the value would be worth the cost of
>> breaking existing code. At the least if this were to go forward I would
>> think we'd want both styles to work even if one was preferred or the other
>> was deprecated.
>>
>>
>>
>> On Dec 26, 2016, at 12:41 PM, Derrick Ho via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> I personally do not see anything wrong with its current placement.
>>
>> It may be there because it was based on an existing cocoa pattern from
>> objective-c
>>
>> - (NSString *)bazWithError:(NSError **)error { ... }
>>
>> Because objective c could only return one thing, using pointer-to-pointer
>> was needed to deliver more than one.
>>
>> When swift came along it became this...
>>
>> func baz(error: NSErrorPointer) -> String
>>
>> The style felt old-fashioned and was replaced with throw.
>>
>> func baz() throws -> String
>>
>>
>> The evolution is consistent.  The pattern is familiar.  I think we should
>> keep the placement of throw as it is.
>>
>> On Mon, Dec 26, 2016 at 9:38 AM thislooksfun via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> Hello Swifters,
>>
>> I've been writing a lot more Swift code recently, and I have found that
>> the default placement of the 'throws' declaration is often confusing,
>> especially to those of us switching from languages where the type of errors
>> thrown is explicitly defined (like Java)
>>
>> For example,
>>
>> // This is pretty clear, this can throw an error
>>
>> func foo() throws
>>
>> { ... }
>>
>>
>>
>> // Also pretty clear, this returns a String
>>
>> func bar() -> String
>>
>> { ... }
>>
>>
>>
>> // Confusing. Does this throw a String? Does it return a String? Does it do both?
>>
>> // I personally keep reading this as 'this can throw a String'
>>
>> func baz() throws -> String
>>
>>
>>
>> // Equivalent code in Java (not a model, just for clarification of why the above is confusing)
>>
>> String baz() throws StringFormatException
>>
>> I therefore suggest either tweaking the syntax around, or moving, the
>> `throws` keyword to avoid this confusion.
>>
>> Some ideas I've had:
>>
>> // Add a comma to separate them
>>
>> func baz() throws, -> String
>>
>>
>>
>> // Move `throws` to the end
>>
>> func baz() -> String throws
>>
>>
>>
>> // Change it to a prefix modifier (like `mutating`)
>>
>> throwing func baz() -> String
>>
>> I'm still not sold on any of the above syntaxes, but I would love to hear
>> your feedback.
>>
>> This would affect existing code, but it would be a fairly small change
>> that would result in very large readability improvements, especially for
>> newcomers, and *especially* for those coming for a language such as Java.
>>
>> -thislooksfun (tlf)
>>
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>>
>>
>> swift-evolution mailing list
>>
>>
>> swift-evolution at swift.org
>>
>>
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>>
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20161226/2231388f/attachment.html>