[swift-evolution] [Pitch] Constrains for numeric types: Int<1...10> Double<0.0...1.0>

Wed May 18 12:28:39 CDT 2016

Or just $0 as in closures or newValue as in setters?

BTW this proposal would be simpler to implement IMHO, since the following code:

var user: MNUser where #statement

Would just become

var user: MNUser {
    didSet { assert(#statement) }
}

And with regular arguments, these assertions would get prepended to the funtion body.

It would get a bit more complicated were this on protocols:

protocol MyProtocol {
   var alpha: Double where alpha >= 0.0 { get set }
}

18. 5. 2016 v 19:18, Vladimir.S via swift-evolution <swift-evolution at swift.org>:

> Also though about this. As for numbers, this could be used:
> 
> var alpha: Double where (0.0...1.0).contains(alpha)
> 
> or
> 
> var value: Int where value.isIn(0..<100)
> 
> if we have
> 
> extension Int {
>    func isIn(i: HalfOpenInterval<Int>)->Bool {
>        return i.contains(self)
>    }
> }
> (it is sad that we can't use `in` name for such function)
> 
> But I don't like here repeats of the name of variable/property. In case small names it is OK, but when we use someDescriptiveName - I don't want to repeat them and IMO any repeat is a possibility for error(when you by mistake typed other name). So probably I'd like something like placeholder #it for the same name:
> 
> var user: MNUser where #it.isLoggedIn
> 
> 
> 
>> On 18.05.2016 19:34, Krystof Vasa via swift-evolution wrote:
>> How about something like this instead? Seems a bit more general and perhaps
>> more useful (though with numbers it's not as elegant)?
>> 
>> var alpha: Double where alpha >= 0.0 && alpha <= 0.0
>> var user: MNUser where user.isLoggedIn
>> var name: String where !name.isEmpty
>> 
>> Krystof
>> 
>>> On May 18, 2016, at 2:49 PM, Adrian Zubarev via swift-evolution
>>> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> As you guys brought my idea back to life and I’ve done some effort of
>>> digging into the Swifts generic future I can show you some fresh ideas.
>>> 
>>> `Refinement Types` could be really handy, but put them aside for a moment.
>>> 
>>> Actually we could achieve something like Int<minValue, maxValue> in Swift
>>> 3. Take a look at this section
>>> here: https://github.com/apple/swift/blob/master/docs/GenericsManifesto.md#generic-value-parameters
>>> 
>>> There is a slightly problem with this, we cannot rewrite all types to be
>>> generic with default parameters. That said it would be nice if we could
>>> overload types somehow (Int vs. Int<Range>), but I’m not sure if this
>>> idea would suit the language like this.
>>> 
>>> Anyways we could then have:
>>> 
>>> struct Int<_ range: Range<Int>> { … }
>>> 
>>> Sadly this makes the type not safe at compile time but only signals the
>>> user that at runtime you can’t use any number our of its range.
>>> 
>>> --
>>> Adrian Zubarev
>>> Sent with Airmail
>>> 
>>> Am 18. Mai 2016 bei 14:13:09, Vladimir.S via swift-evolution
>>> (swift-evolution at swift.org <mailto:swift-evolution at swift.org>) schrieb:
>>> 
>>>> > I generally think it’s a cool idea and that it can be useful in minimizing
>>>> > partial functions by requiring that these cases are explicitly handled.
>>>> 
>>>> Support this opinion.
>>>> 
>>>> Other example where such feature could be useful: some public property in
>>>> type that can accept values from some interval. For example we have class
>>>> with transparency property that can be 0.0 ... 0.1:
>>>> 
>>>> class MyShape {
>>>> public var transparency: Double = 1.0 // 0.0 ... 0.1
>>>> }
>>>> 
>>>> yes, we can use willSet/didSet to check this every time. But if we have a
>>>> number of such properties, we have a lot of repetitive and boilerplate code:
>>>> 
>>>> class C {
>>>> var transparancy : Double = 1.0 {
>>>> didSet { check(transparancy, 0.0...1.0) }
>>>> }
>>>> 
>>>> var prop1 : Int = 1 {
>>>> didSet { check(prop1, from: -10...10) }
>>>> }
>>>> 
>>>> var prop2 : Int = 1 {
>>>> didSet { check(prop2, from: 0...100) }
>>>> }
>>>> }
>>>> 
>>>> , and all will be worse if we also need didSet observers to do some
>>>> 'useful' work here.
>>>> Proposed solution will looks like:
>>>> 
>>>> class C {
>>>> var transparancy : Double<0.0...1.0> = 1.0
>>>> 
>>>> var prop1 : Int<-10...10> = 1
>>>> 
>>>> var prop2 : Int<0...100> = 1
>>>> }
>>>> 
>>>> Probably the alternative could be some kind of `where` or `bounded` clause
>>>> for numeric types and arguments:
>>>> 
>>>> class C {
>>>> var transparancy : Double = 1.0 where 0.0...1.0
>>>> //var transparancy : Double bounded 0.0...1.0 = 1.0
>>>> 
>>>> var prop1 : Int = 1 where -10...10
>>>> 
>>>> var prop2 : Int = 1 where 0.0...1.0
>>>> 
>>>> //var prop3 : Float bounded 0.0..<100.0 = 0.0
>>>> }
>>>> 
>>>> 
>>>> On 18.05.2016 11:30, David Rönnqvist via swift-evolution wrote:
>>>> > It reminds me of "Refinement Types" (see for example [this blog post][1] or
>>>> > [this paper][2]).
>>>> >
>>>> > I generally think it’s a cool idea and that it can be useful in minimizing
>>>> > partial functions by requiring that these cases are explicitly handled.
>>>> > For example, highlighting that the following `average` implementation
>>>> > divides by zero when the list is empty:
>>>> >
>>>> > func average(numbers: [Int]) -> Int {
>>>> > return sum(numbers) / numbers.count
>>>> > }
>>>> >
>>>> >
>>>> > and requiring that the empty list case is handled separately:
>>>> >
>>>> > func average(numbers: [Int]) -> Int {
>>>> > guard !numbers.isEmpty else { return 0 }
>>>> > return sum(numbers) / numbers.count
>>>> > }
>>>> >
>>>> >
>>>> > Regards,
>>>> > David
>>>> >
>>>> > [1]: http://goto.ucsd.edu/~rjhala/liquid/haskell/blog/blog/2013/01/01/refinement-types-101.lhs/
>>>> <http://goto.ucsd.edu/%7Erjhala/liquid/haskell/blog/blog/2013/01/01/refinement-types-101.lhs/>
>>>> > <http://goto.ucsd.edu/%7Erjhala/liquid/haskell/blog/blog/2013/01/01/refinement-types-101.lhs/>
>>>> > [2]: http://goto.ucsd.edu/~nvazou/refinement_types_for_haskell.pdf
>>>> <http://goto.ucsd.edu/%7Envazou/refinement_types_for_haskell.pdf>
>>>> > <http://goto.ucsd.edu/%7Envazou/refinement_types_for_haskell.pdf>
>>>> >
>>>> >
>>>> >> On 11 May 2016, at 20:00, Adrian Zubarev via swift-evolution
>>>> >> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>>> <mailto:swift-evolution at swift.org>> wrote:
>>>> >>
>>>> >> Okay I’m fine with that for now. If you’d have to decide on some syntax
>>>> >> for such a future, how would it look like? I’m just curious.
>>>> >>
>>>> >> I tend to square brackets Double[0.0 … 1.0], because otherwise it might
>>>> >> look like a generic type, but I’m not sure if this type refinement could
>>>> >> be applied to other types as well so we actually would stick to the
>>>> >> generic type syntax here Float<-1.0 … 1.0>.
>>>> >>
>>>> >> --
>>>> >> Adrian Zubarev
>>>> >> Sent with Airmail
>>>> >>
>>>> >> Am 11. Mai 2016 bei 19:54:09, Matthew Johnson (matthew at anandabits.com <mailto:matthew at anandabits.com>
>>>> >> <mailto:matthew at anandabits.com>) schrieb:
>>>> >>
>>>> >>> This is called a refinement type. It would be cool to explore that
>>>> >>> direction in the future but it is definitely well out of scope for Swift 3.
>>>> >>>
>>>> >>> Sent from my iPad
>>>> >>>
>>>> >>> On May 11, 2016, at 12:45 PM, Adrian Zubarev via swift-evolution
>>>> >>> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>>> <mailto:swift-evolution at swift.org>> wrote:
>>>> >>>
>>>> >>>> Hello Swift community. I'd like to discuss with you if we need
>>>> >>>> something like this in Swift 3 or any future Swift version.
>>>> >>>>
>>>> >>>> As you may know there is no way to constrain a numeric type expect for
>>>> >>>> some scope internal assertion or precodintions which may produce a
>>>> >>>> runtime error if the input value is out of the defined bound.
>>>> >>>>
>>>> >>>> func foo(value: Int) {
>>>> >>>> assert(value > 0 && value <= 10)
>>>> >>>>
>>>> >>>> // passed
>>>> >>>> }
>>>> >>>>
>>>> >>>> How would it be if Swift would allow us to constraint numeric typs with
>>>> >>>> ranges/intervals?
>>>> >>>>
>>>> >>>> func newFoo(value: Int<1...10>) {
>>>> >>>> // no need for an assertion any more
>>>> >>>> }
>>>> >>>>
>>>> >>>> We could go even further and add more then one range/interval:
>>>> >>>>
>>>> >>>> func someFoo(value: Int<0...20, 40...60>) { /* do some work */ }
>>>> >>>>
>>>> >>>> Not only integers should have this ability but also floating point
>>>> >>>> types like Double and Float.
>>>> >>>>
>>>> >>>> Alternative form might look like this:
>>>> >>>>
>>>> >>>> Double[1.0...10.0]
>>>> >>>> Float[0.0...1.0, 10.0...100.0]
>>>> >>>>
>>>> >>>> One downside of half opened ranges/intervals is the left side of its
>>>> >>>> set. How do we exclude the left element?
>>>> >>>>
>>>> >>>> 1...10 means 1..<11 equals [1, 11)
>>>> >>>>
>>>> >>>> But how can we create something like (0.0, 1.0), do we need a strange
>>>> >>>> looking binary operator 0.0>..<1.0?
>>>> >>>>
>>>> >>>> What do you think? I'd love to hear any feedback to this.
>>>> >>>>
>>>> >>>> --
>>>> >>>> Adrian Zubarev
>>>> >>>> Sent with Airmail
>>>> >>>> _______________________________________________
>>>> >>>> swift-evolution mailing list
>>>> >>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>>> <mailto:swift-evolution at swift.org>
>>>> >>>> https://lists.swift.org/mailman/listinfo/swift-evolution
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>>>> >
>>>> >
>>>> >
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