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

[Tim Vermeulen]

> 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.
> 
> 
> 

Well, this change would render a big part of the naming guidelines meaningless, but isn’t that a good thing? Guidelines are often in place to prevent ambiguity, and this solution would do that without the need for guidelines.

Anyways, I wouldn’t be surprised if this idea has come up before and has been rejected, but to me it sounds like a good idea.