[swift-evolution] mutating/non-mutating suggestion from a Rubyist

James Froggatt conductator at ntlworld.com
Sun Apr 24 10:38:34 CDT 2016

The idea of distinguishing all mutating/non-mutating functions with only the assignment operator did occur to me as I wrote that.
Using such a rule would allow automatic generation of mutating methods from non-mutating ones, since the naming would no longer need changing.
However, this would also mean scrapping half the Naming Guidelines, so I'm hesitant to put that possibility forward as a serious proposal.

I think union (verb) vs union (noun) would work as a one off, though, since it fits the guidelines as they currently stand. It would be a nice way to demonstrate that the compiler can make the distinction in a public API.

From James F

On 24 Apr 2016, at 15:49, Tim Vermeulen <tvermeulen at me.com> wrote:

>> The whole naming issue seems to be caused by the .union(_:) function. The Swift Guidelines say that mutating functions should use a verb, and non-mutating forms should use a noun, but in this case, the word union itself is a verb and a noun.
>> Have we considered this, then:
>> a.union(b) //mutating
>> _ = a.union(b) //non-mutating
>> There is no ambiguity in most situations, and the fact the Swift compiler can't disambiguate this at the moment is a bug I'd like to see fixed in the Swift 3 timeframe. I think this wouldn't be such a bad compromise, and other functions could still use the standard -ed/-ing system alongside this without the API looking inconsistent, unlike with the form- prefix.
>> Admittedly, there is merit to the idea that functional methods should make non-mutating forms the primary form, but I feel like we should figure out what our stance is on this methodology in general. A mention in the Guidelines one way or the other would be nice, since the current rules seem to support this.
>>> From James F
> Can’t we do this for every mutating method? i.e.
> var numbers = [1,3,2]
> let sorted = numbers.sort()
> // sorted is [1,2,3], numbers is [1,3,2]
> numbers.sort()
> // numbers is [1,2,3]
> I suppose this would require that the mutating version doesn’t return anything, and I don’t know if that’s ever a problem.

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