# [swift-evolution] [Proposal] Random Unification

Nate Cook natecook at apple.com
Thu Nov 30 18:55:05 CST 2017

```> On Nov 30, 2017, at 6:20 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>
> On Thu, Nov 30, 2017 at 5:24 PM, Nate Cook <natecook at apple.com> wrote:
>>> On Nov 30, 2017, at 4:30 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
>>>
>>>> On Thu, Nov 30, 2017 at 3:58 PM, Dave DeLong via swift-evolution <swift-evolution at swift.org> wrote:
>>>>
>>>>
>>>>> On Nov 30, 2017, at 2:48 PM, Jonathan Hull via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>
>>>>> I would personally go with:
>>>>>
>>>>> 	Int.random //Returns a random Int
>>>>
>>>> “Type.random” is so rarely used as to not be worth the addition, IMO. If you really need a random element from the *entire* domain, then I think you should have to manually create the ClosedRange<T> yourself.
>>>>
>>>>> 	Int.random(in: ClosedRange<Int>) //Works for Comparable types. Gives a result from the closed range. Closed Range is never empty.
>>>>
>>>> This is redundant. In order to pick a random element, you’re saying I should have to do “Int.random(0 ..< 10)”? The redundancy here is that I have to specify Int twice: once for the “.random” call, and again for the type of the range. We can do better than that.
>>
>> I don’t see how this is redundant—do you mean that you’d need to write out the type name instead of writing `(0..<10).random()!`? I continue to be of the opinion that picking a random integer/floating-point value/Boolean and picking a random element from a collection are two different operations. Yes, there’s overlap between the two, but they’re different enough that having two ways to choose an integer between 0 and 10 would be fine.
>
> As I wrote elsewhere, if they're sufficiently different enough, then they ought to have distinct names. If they are not, then there ought to be only one of them. I'm no longer sure myself of which one I'd prefer, but in no case should there be two things named "random."
>
> If the proposal to make `IndexDistance == Int` is accepted, then ranges cannot conform to Collection and we encounter some interesting difficulties attempting to index into such a collection to pick a random value.
>
>>>>> 	[0,2,3].randomElement //Returns a random element from the collection
>>>>
>>>> I strongly believe this should be a method, not a property. Properties, like .first and .last, are expected to return the same value each time you access them. “.random” inherently breaks that.
>>>
>>> FWIW--and this isn't a vote, I know--I largely agree with Dave DeLong's conclusions above, and for substantially the same reasons.
>>>>>
>>>>> Then a version of each with a ‘using:’ parameter which takes a generator/source:
>>>>>
>>>>> 	Int.random(using: RandomSource) //Returns a random Int using the given source of randomness
>>>>> 	Int.random(in: ClosedRange<Int>, using: RandomSource)
>>>>> 	[0,2,3].randomElement(using: RandomSource)
>>>>>
>>>>> In my own RandomSource & RandomSourceCreatable protocols, I frequently use random colors and sizes as well.  The issue there is that you really want a closed range for each dimension. I wish Swift had a better notion of dimensionality baked into the language.
>>>>>
>>>>> What I ended up doing was having a “constraints” parameter which took an array of constraints which corresponded to various dimensions.  It works for me, but it might be a bit complex for something in the standard library.
>>>>>
>>>>> Honestly, given the current capabilities of Swift what this really calls for is custom initializers/functions for dimensional types:
>>>>>
>>>>> 	UIColor.random //This comes from the protocol
>>>>> 	UIColor.random(hue: ClosedRange<CGFloat> = 0…1, saturation: ClosedRange<CGFloat> = 0…1, brightness: ClosedRange<CGFloat> = 0…1, alpha: ClosedRange<CGFloat> = 1…1)
>>>>> 	//…and of course the same as above, but with ‘using:'
>>>>>
>>>>> Then you can easily get random colors which look like they belong together:
>>>>>
>>>>> 	let myColor = UIColor.random(saturation: 0.2…0.2, brightness: 0.6…0.6)
>>>>>
>>>>> There would probably also be a convenience version taking CGFloats and passing them to the real function as ranges:
>>>>>
>>>>> 	let myColor = UIColor.random(saturation: 0.2, brightness: 0.6)
>>>>>
>>>>>
>>>>> This means that our default RandomSource needs to be publicly available, so that the custom functions can use it as the default…
>>>
>>> It does not. Having actually implemented some version of these APIs, it's readily apparent now to me that all custom types can simply call Int.random(in:) (or UnsafeRawBufferPointer<T>.random(byteCount:), or whatever else we want to have in the standard library) to get random values from the default RNG for any built-in type and size. The actual default random need never be exposed publicly, and since its functions are strictly redundant to these other APIs (which, of course, are the "currency" APIs that our purpose here is to design and make public), the default random is required only for internal implementation of the "currency" APIs and (a) is better off *not* exposed; (b) doesn't need to be of the same type as other RNGs, conform to the same protocols, or for that matter, does not even need to be a type or be written in Swift.
>>
>> Assuming we have two versions of whatever new random operations we add, where one takes an RNG as a parameter and the other uses the default, how would I add functionality that matches this pattern in my own code? The standard library would look have code like this:
>>
>>     extension MutableCollection {
>>         func shuffle(using rng: RNG) {
>>             // shuffle the elements
>>         }
>>
>>         func shuffle() {
>>             shuffle(using: _privateDefaultRNG)
>>         }
>>     }
>>
>> Let’s say I’m writing something for my own app or library, and want to add two related methods with the same pattern:
>>
>>     extension Collection {
>>         func randomRange(length: Int, using rng: RNG) -> [SubSequence] {
>>             // select a starting point in 0..<count - length
>>             // verify that florps are still sideways
>>             // etc
>>         }
>>
>>         func randomRange(length: Int) {
>>             return randomRange(length: Int, using: ?????)
>>         }
>>     }
>>
>> What do I put in the second method so I don’t have to implement this twice?
>
> If this is to be used, as others say, to permit obtaining a random value of a certain distribution passed in as the parameter `using`, then to implement it correctly you *must* implement it twice. Actually, you may have to implement it not just twice but differently for each distribution, so I'm not sure that it's a viable design for the stated use case.

I don't think I've seen anyone propose that you would haven't different distributions by passing different RNGs. Is there any way any of this works for an RNG that isn't providing uniform random bits? I don't understand how any of these primitive methods would work with an RNG that was doing something different, regardless of how the methods are spelled. The purpose of the (using:) versions is to allow for RNGs that meet different requirements from the default: seedable/repeatable, faster, more secure, etc.

>
>> -Nate
>>
>>
>>>> 👍
>>>>
>>>>>
>>>>> Thanks,
>>>>> Jon
>>>>>
>>>>>
>>>>>> On Nov 27, 2017, at 10:14 AM, TellowKrinkle via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>>
>>>>>> You say that all the `.random`s have different semantics, but to me (at least), they are all very similar.  All the methods can be summarized as selecting a single random element from a collection
>>>>>> `[0, 2, 3].random` selects a single element from the given collection
>>>>>> `Int.random(in: 0…8)` selects a single element from the given range
>>>>>> `Int.random` has no range, but selects a single element from the collection of all ints (equivalent to if the above method had a default value for its range)
>>>>>> So to me these are all doing the same operation, just with different types of inputs
>>>>>>
>>>>>>> 2017/11/24 20:07、Alejandro Alonso <aalonso128 at outlook.com>のメール:
>>>>>>>
>>>>>>>
>>>>>>> - Alejandro
>>>>>>>
>>>>>>> ---------- Forwarded message ----------
>>>>>>> From: Xiaodi Wu <xiaodi.wu at gmail.com>
>>>>>>> Date: Nov 24, 2017, 3:05 PM -0600
>>>>>>> To: Alejandro Alonso <aalonso128 at outlook.com>
>>>>>>> Cc: Brent Royal-Gordon <brent at architechies.com>, Steve Canon via swift-evolution <swift-evolution at swift.org>
>>>>>>> Subject: Re: [swift-evolution] [Proposal] Random Unification
>>>>>>>
>>>>>>>> On Fri, Nov 24, 2017 at 2:55 PM, Alejandro Alonso  <aalonso128 at outlook.com> wrote:
>>>>>>>>> Regarding naming too many things “random”, I’ve talked to many developers on my end and they all don’t find it confusing. This proposal is aimed to make it obvious what the operation is doing when regarding random. I still agree that the proposed solution does just that and in practice feels good to write.
>>>>>>>>
>>>>>>>> I must disagree quite strongly here. The various facilities you name "random" have different semantics, and differences in semantics should be reflected in differences in names. It doesn't matter that some people don't find it confusing; it is objectively the case that you have named multiple distinct facilities with the same name, which leads to confusion. I, for one, get confused, and you can see on this list that people are using arguments about one property named "random" to discuss another property named "random". This is quite an intolerable situation.
>>>>>>>>
>>>>>>>>> I disagree that sample is the correct naming to use here. Getting a sample is a verb in this context which would make it break API guidelines just as well as `pick()`. To sample is to “take a sample or samples of (something) for analysis.” I can agree to use `sampling()` which follows API guidelines. This would result in the following grammar for `[“hi”, “hello”, “hey”].sampling(2)`, “From array, get a sampling of 2"
>>>>>>>>
>>>>>>>> "Sampling" is fine.
>>>>>>>>
>>>>>>>>
>>>>>>>>>> On Nov 23, 2017, 12:54 AM -0600, Xiaodi Wu , wrote:
>>>>>>>>>>> On Wed, Nov 22, 2017 at 23:01 Alejandro Alonso <aalonso128 at outlook.com> wrote:
>>>>>>>>>>> Like I’ve said, python has different syntax grammar. We have to read each call site and form a sentence from it. `random.choice([1, 2, 3])` to me this reads, “Get a random choice from array”. This makes sense. Slapping the word choice as an instance property like `[1, 2, 3].choice` reads, “From array, get choice”. What is choice? This doesn’t make sense at all to me. To me, the only good solution is `[1, 2, 3].random` which reads, “From array, get random”. I actually think most users will be able to understand this at first glance rather than choice (or any or some).
>>>>>>>>>>
>>>>>>>>>> Again, my concern here is that you are proposing to name multiple things "random". If this property should be called "random"--which I'm fine with--then the static method "random(in:)" should be named something else, and the static property "random" should be dropped altogether (as I advocate for reasons we just discussed) or renamed as well. It is simply too confusing that there are so many different "random" methods or properties. Meanwhile, isn't your default RNG also going to be called something like "DefaultRandom"?
>>>>>>>>>>
>>>>>>>>>>> In regards to the sample() function on collections, I have added this as I do believe this is something users need. The name I gave it was pick() as this reads, “From array, pick 2”.
>>>>>>>>>>
>>>>>>>>>> The name "sample" has been used to good effect in other languages, has a well understood meaning in statistics, and is consistent with Swift language guidelines. The operation here is a sampling, and per Swift guidelines the name must be a noun: therefore, 'sample' is fitting. "Pick" does not intrinsically suggest randomness, whereas sample does, and your proposed reading uses it as a verb, whereas Swift guidelines tell us it must be a noun. I would advocate strongly for using well-established terminology and sticking with "sample."
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> On Nov 17, 2017, 8:32 PM -0600, Xiaodi Wu via swift-evolution <swift-evolution at swift.org>, wrote:
>>>>>>>>>>>> On Fri, Nov 17, 2017 at 7:11 PM, Brent Royal-Gordon <brent at architechies.com> wrote:
>>>>>>>>>>>>>> On Nov 17, 2017, at 3:09 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> But actually, Int.random followed by % is the much bigger issue and a very good cautionary tale for why T.random is not a good idea. Swift should help users do the correct thing, and getting a random value across the full domain and computing an integer modulus is never the correct thing to do because of modulo bias, yet it's a very common error to make. We are much better off eliminating this API and encouraging use of the correct API, thereby reducing the likelihood of users making this category of error.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Amen.
>>>>>>>>>>>>>
>>>>>>>>>>>>>> If (and I agree with this) the range-based notation is less intuitive (0..<10.random is certainly less discoverable than Int.random), then we ought to offer an API in the form of `Int.random(in:)` but not `Int.random`. This does not preclude a `Collection.random` API as Alejandro proposes, of course, and that has independent value as Gwendal says.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> If we're not happy with the range syntax, maybe we should put `random(in:)`-style methods on the RNG protocol as extension methods instead. Then there's a nice, uniform style:
>>>>>>>>>>>>>
>>>>>>>>>>>>> let diceRoll = rng.random(in: 1...6)
>>>>>>>>>>>>> let card = rng.random(in: deck)
>>>>>>>>>>>>> let isHeads = rng.random(in: [true, false])
>>>>>>>>>>>>> let probability = rng.random(in: 0.0...1.0)
>>>>>>>>>>>>>
>>>>>>>>>>>>> // Special FloatingPoint overload
>>>>>>>>>>>>>
>>>>>>>>>>>>> The only issue is that this makes the default RNG's name really important. Something like:
>>>>>>>>>>>>>
>>>>>>>>>>>>> DefaultRandom.shared.random(in: 1...6)
>>>>>>>>>>>>>
>>>>>>>>>>>>> Will be a bit of a pain for users.
>>>>>>>>>>>>
>>>>>>>>>>>> I did in fact implement this style of RNG in NumericAnnex, but I'm not satisfied with the design myself. Not only is it a bit of an ergonomic thorn, there's also another drawback that actually has weighty implications:
>>>>>>>>>>>>
>>>>>>>>>>>> Users aren't conditioned to reuse RNG instances. Perhaps, it is because it can "feel" wrong that multiple random instances should come from the *same* RNG. Instead, it "feels" more right to initialize a new RNG for every random number. After all, if one RNG is random, two must be randomer! This error is seen with some frequency in other languages that adopt this design, and they sometimes resort to educating users through documentation that isn't consistently heeded.
>>>>>>>>>>>>
>>>>>>>>>>>> Of course, you and I both know that this is not ideal for performance. Moreover, for a number of PRNG algorithms, the first few hundred or thousand iterations can be more predictable than later iterations. (Some algorithms discard the first n iterations, but whether that's adequate depends on the quality of the seed, IIUC.) Both of these issues don't apply specifically to a default RNG type that cannot be initialized and always uses entropy from the global pool, but that's not enough to vindicate the design, IMO. By emphasizing *which* RNG instance is being used for random number generation, the design encourages non-reuse of non-default RNGs, which is precisely where this common error matters for performance (and maybe security).
>>>>>>>>>>>>
>>>>>>>>>>>>> Maybe we call the default RNG instance `random`, and then give the `random(in:)` methods another name, like `choose(in:)`?
>>>>>>>>>>>>>
>>>>>>>>>>>>> let diceRoll = random.choose(in: 1...6)
>>>>>>>>>>>>> let card = random.choose(in: deck)
>>>>>>>>>>>>> let isHeads = random.choose(in: [true, false])
>>>>>>>>>>>>> let probability = random.choose(in: 0.0...1.0)
>>>>>>>>>>>>> let diceRoll = rng.choose(in: 1...6)
>>>>>>>>>>>>> let card = rng.choose(in: deck)
>>>>>>>>>>>>> let isHeads = rng.choose(in: [true, false])
>>>>>>>>>>>>> let probability = rng.choose(in: 0.0...1.0)
>>>>>>>>>>>>>
>>>>>>>>>>>>> This would allow us to keep the default RNG's type private and expose it only as an existential—which means more code will treat RNGs as black boxes, and people will extend the RNG protocol instead of the default RNG struct—while also putting our default random number generator under the name `random`, which is probably where people will look for such a thing.
>>>>>>>>>>>>
>>>>>>>>>>>> I've said this already in my feedback, but it can get lost in the long chain of replies, so I'll repeat myself here because it's relevant to the discussion. I think one of the major difficulties of discussing the proposed design is that Alejandro has chosen to use a property called "random" to name multiple distinct functions which have distinct names in other languages. In fact, almost every method or function is being named "random." We are tripping over ourselves and muddling our thinking (or at least, I find myself doing so) because different things have the exact same name, and if I'm having this trouble after deep study of the design, I think it's a good sign that this is going to be greatly confusing to users generally.
>>>>>>>>>>>>
>>>>>>>>>>>> First, there's Alejandro's _static random_, which he proposes to return an instance of type T given a type T. In Python, this is named `randint(a, b)` for integers, and `random` (between 0 and 1) or `uniform(a, b)` for floating-type types. The distinct names reflect the fact that `randint` and `uniform` are mathematically quite different (one samples a *discrete* uniform distribution and the other a *continuous* uniform distribution), and I'm not aware of non-numeric types offering a similar API in Python. These distinct names accurately reflect critiques from others on this list that the proposed protocol `Randomizable` lumps together types that don't share any common semantics for their _static random_ method, and that the protocol is of questionable utility because types in general do not share sufficient semantics such that one can do interesting work in generic code with such a protocol.
>>>>>>>>>>>>
>>>>>>>>>>>> Then there's Alejandro's _instance random_, which he proposes to return an element of type T given a instance of a collection of type T. In Python, this is named "choice(seq)" (for one element, or else throws an error) and "sample(seq, k)" (for up to k elements). As I noted, Alejandro was right to draw an analogy between _instance random_ and other instance properties of a Collection such as `first` and `last`. In fact, the behavior of Python's "choice" (if modified to return an Optional) and "sample", as a pair, would fit in very well next to Swift's existing pairs of `first` and `prefix(k)` and `last` and `suffix(k)`. We could trivially Swiftify the names here; for example:
>>>>>>>>>>>>
>>>>>>>>>>>> ```
>>>>>>>>>>>> [1, 2, 3].first
>>>>>>>>>>>> [1, 2, 3].any // or `choice`, or `some`, or...
>>>>>>>>>>>> [1, 2, 3].last
>>>>>>>>>>>>
>>>>>>>>>>>> [1, 2, 3].prefix(2)
>>>>>>>>>>>> [1, 2, 3].sample(2)
>>>>>>>>>>>> [1, 2, 3].suffix(2)
>>>>>>>>>>>> ```
>>>>>>>>>>>>
>>>>>>>>>>>> I'm going to advocate again for _not_ naming all of these distinct things "random". Even in conducting this discussion, it's so hard to keep track of what particular function a person is giving feedback about.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>> swift-evolution mailing list
>>>>>>>>>>>> swift-evolution at swift.org
>>>>>>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>>>>>
>>>>>>>>> On Nov 17, 2017, 8:32 PM -0600, Xiaodi Wu via swift-evolution <swift-evolution at swift.org>, wrote:
>>>>>>>>>
>>>>>>>>>> On Fri, Nov 17, 2017 at 7:11 PM, Brent Royal-Gordon <brent at architechies.com> wrote:
>>>>>>>>>>>> On Nov 17, 2017, at 3:09 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>> But actually, Int.random followed by % is the much bigger issue and a very good cautionary tale for why T.random is not a good idea. Swift should help users do the correct thing, and getting a random value across the full domain and computing an integer modulus is never the correct thing to do because of modulo bias, yet it's a very common error to make. We are much better off eliminating this API and encouraging use of the correct API, thereby reducing the likelihood of users making this category of error.
>>>>>>>>>>>
>>>>>>>>>>> Amen.
>>>>>>>>>>>
>>>>>>>>>>>> If (and I agree with this) the range-based notation is less intuitive (0..<10.random is certainly less discoverable than Int.random), then we ought to offer an API in the form of `Int.random(in:)` but not `Int.random`. This does not preclude a `Collection.random` API as Alejandro proposes, of course, and that has independent value as Gwendal says.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> If we're not happy with the range syntax, maybe we should put `random(in:)`-style methods on the RNG protocol as extension methods instead. Then there's a nice, uniform style:
>>>>>>>>>>>
>>>>>>>>>>> let diceRoll = rng.random(in: 1...6)
>>>>>>>>>>> let card = rng.random(in: deck)
>>>>>>>>>>> let isHeads = rng.random(in: [true, false])
>>>>>>>>>>> let probability = rng.random(in: 0.0...1.0)
>>>>>>>>>>>
>>>>>>>>>>> // Special FloatingPoint overload
>>>>>>>>>>>
>>>>>>>>>>> The only issue is that this makes the default RNG's name really important. Something like:
>>>>>>>>>>>
>>>>>>>>>>> DefaultRandom.shared.random(in: 1...6)
>>>>>>>>>>>
>>>>>>>>>>> Will be a bit of a pain for users.
>>>>>>>>>>
>>>>>>>>>> I did in fact implement this style of RNG in NumericAnnex, but I'm not satisfied with the design myself. Not only is it a bit of an ergonomic thorn, there's also another drawback that actually has weighty implications:
>>>>>>>>>>
>>>>>>>>>> Users aren't conditioned to reuse RNG instances. Perhaps, it is because it can "feel" wrong that multiple random instances should come from the *same* RNG. Instead, it "feels" more right to initialize a new RNG for every random number. After all, if one RNG is random, two must be randomer! This error is seen with some frequency in other languages that adopt this design, and they sometimes resort to educating users through documentation that isn't consistently heeded.
>>>>>>>>>>
>>>>>>>>>> Of course, you and I both know that this is not ideal for performance. Moreover, for a number of PRNG algorithms, the first few hundred or thousand iterations can be more predictable than later iterations. (Some algorithms discard the first n iterations, but whether that's adequate depends on the quality of the seed, IIUC.) Both of these issues don't apply specifically to a default RNG type that cannot be initialized and always uses entropy from the global pool, but that's not enough to vindicate the design, IMO. By emphasizing *which* RNG instance is being used for random number generation, the design encourages non-reuse of non-default RNGs, which is precisely where this common error matters for performance (and maybe security).
>>>>>>>>>>
>>>>>>>>>>> Maybe we call the default RNG instance `random`, and then give the `random(in:)` methods another name, like `choose(in:)`?
>>>>>>>>>>>
>>>>>>>>>>> let diceRoll = random.choose(in: 1...6)
>>>>>>>>>>> let card = random.choose(in: deck)
>>>>>>>>>>> let isHeads = random.choose(in: [true, false])
>>>>>>>>>>> let probability = random.choose(in: 0.0...1.0)
>>>>>>>>>>> let diceRoll = rng.choose(in: 1...6)
>>>>>>>>>>> let card = rng.choose(in: deck)
>>>>>>>>>>> let isHeads = rng.choose(in: [true, false])
>>>>>>>>>>> let probability = rng.choose(in: 0.0...1.0)
>>>>>>>>>>>
>>>>>>>>>>> This would allow us to keep the default RNG's type private and expose it only as an existential—which means more code will treat RNGs as black boxes, and people will extend the RNG protocol instead of the default RNG struct—while also putting our default random number generator under the name `random`, which is probably where people will look for such a thing.
>>>>>>>>>>
>>>>>>>>>> I've said this already in my feedback, but it can get lost in the long chain of replies, so I'll repeat myself here because it's relevant to the discussion. I think one of the major difficulties of discussing the proposed design is that Alejandro has chosen to use a property called "random" to name multiple distinct functions which have distinct names in other languages. In fact, almost every method or function is being named "random." We are tripping over ourselves and muddling our thinking (or at least, I find myself doing so) because different things have the exact same name, and if I'm having this trouble after deep study of the design, I think it's a good sign that this is going to be greatly confusing to users generally.
>>>>>>>>>>
>>>>>>>>>> First, there's Alejandro's _static random_, which he proposes to return an instance of type T given a type T. In Python, this is named `randint(a, b)` for integers, and `random` (between 0 and 1) or `uniform(a, b)` for floating-type types. The distinct names reflect the fact that `randint` and `uniform` are mathematically quite different (one samples a *discrete* uniform distribution and the other a *continuous* uniform distribution), and I'm not aware of non-numeric types offering a similar API in Python. These distinct names accurately reflect critiques from others on this list that the proposed protocol `Randomizable` lumps together types that don't share any common semantics for their _static random_ method, and that the protocol is of questionable utility because types in general do not share sufficient semantics such that one can do interesting work in generic code with such a protocol.
>>>>>>>>>>
>>>>>>>>>> Then there's Alejandro's _instance random_, which he proposes to return an element of type T given a instance of a collection of type T. In Python, this is named "choice(seq)" (for one element, or else throws an error) and "sample(seq, k)" (for up to k elements). As I noted, Alejandro was right to draw an analogy between _instance random_ and other instance properties of a Collection such as `first` and `last`. In fact, the behavior of Python's "choice" (if modified to return an Optional) and "sample", as a pair, would fit in very well next to Swift's existing pairs of `first` and `prefix(k)` and `last` and `suffix(k)`. We could trivially Swiftify the names here; for example:
>>>>>>>>>>
>>>>>>>>>> ```
>>>>>>>>>> [1, 2, 3].first
>>>>>>>>>> [1, 2, 3].any // or `choice`, or `some`, or...
>>>>>>>>>> [1, 2, 3].last
>>>>>>>>>>
>>>>>>>>>> [1, 2, 3].prefix(2)
>>>>>>>>>> [1, 2, 3].sample(2)
>>>>>>>>>> [1, 2, 3].suffix(2)
>>>>>>>>>> ```
>>>>>>>>>>
>>>>>>>>>> I'm going to advocate again for _not_ naming all of these distinct things "random". Even in conducting this discussion, it's so hard to keep track of what particular function a person is giving feedback about.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> _______________________________________________
>>>>>>>>>> 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
>>
>
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