[swift-evolution] [Proposal] Random Unification

Fri Nov 24 22:59:05 CST 2017

So why is it more important for the random method on a collection to have a special method that guarantees a discrete uniform distribution than it is for an Int?  If you’re going to split on guaranteed-discrete-uniform vs maybe-discrete-uniform, why not split on discrete-uniform vs not-discrete-uniform (note: I would not want either of these)?

Why not just let everything be maybe-discrete-uniform and then specify:
- Things involving discrete sets (including collections and ranges of discrete values like ints) return a discrete uniform distribution
- Things involving continuous ranges (including ranges of floating-point types) return a continuous uniform distribution
I don’t really see the point in differentiating between a discrete and continuous distribution, since it makes no sense to use a continuous distribution for things that are discrete, and it also makes no sense to use a discrete distribution for things that are continuous.

As for optional vs non-optional, I’d say this is similar to conforming to RawRepresentable (where you can implement its `init?(rawValue:)` with an `init(rawValue:)` if your type doesn’t ever fail to initialize) where you’re simply indicating that for whatever reason, your type is less likely to fail than whatever the most likely to fail type is.

Personally, I don’t care whether or not `Int.random` stays, but it’s functionally identical to `Int.random(in:)` with a default argument so it doesn’t make much of a difference for this decision since removing it wouldn’t affect the issue you’re having between `Int.random(in:)` and `Collection.random`.

> 2017/11/24 21:39、Xiaodi Wu <xiaodi.wu at gmail.com>のメール:
> 
> On Fri, Nov 24, 2017 at 9:05 PM, TellowKrinkle <tellowkrinkle at gmail.com <mailto:tellowkrinkle at gmail.com>> wrote:
> You say that all the `.random`s have different semantics, but to me (at least), they are all very similar.
> 
> Of course they are _similar_: this is precisely why it's so important to be clear about the differences in the naming.
>  
> 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
> 
> There are many subtle but important differences. For example:
> 
> `[1, 2, 3].random` is a sampling operation based on a discrete uniform distribution. All operations that choose an element from a Collection would behave similarly: that is, instance `random` guarantees sampling based on a discrete uniform distribution. It does so happen that `Int.random` gives values in a discrete uniform distribution. However, `Float.random` most certainly does not: it would sample from a _continuous_ uniform distribution. In general, static `random` does not guarantee any particular distribution at all. This is a huge semantic distinction.
> 
> Static `random` (e.g., `Int.random`) will always return a value, whereas instance `random` (e.g., `[1, 2, 3].random`) might not. This is because all types that implement static `random` must be instantiable, whereas collections can be empty. One might conclude that it makes sense for static `random` to be of type `T`, whereas instance `random` would be most fittingly of type `T?`. However, because they're both named "random", people have been misled into thinking that they're in fact the same operation and must therefore have the same return type. Alejandro has argued that `[1, 2, 3].random` should be of type `T` *because* it would not be ergonomic for `Int.random` to be of type `T?`. Meanwhile, others have argued that, because `[].random` should be failable, `Int.random` should be as well. This perceived need for the two distinct facilities to return the same type is completely due to them having the same proposed name. However, as described above, one is failable and the other is not *because of their differing semantics*.
> 
> Meanwhile, we have had a debate as to whether `random` should be spelled as a property or a function. Alejandro has argued that `random` is like `first` or `last` and is a property of a collection, while others have argued that `Int.random()` should be spelled like a function because it instantiates a different value each time. Notionally, of course, instance `random` selects one already-existing element from a collection, whereas static `random` creates a new value that doesn't exist yet and truly could be considered like a factory method. However, because again they've both been proposed to have the name "random", people are using arguments about one type of "random" to decide questions of syntax for the other type of "random".
> 
> All of this goes away when we clarify that these two are distinct facilities: they have different semantics. Of course, elsewhere, I've advocated for `Int.random` to be removed altogether due to large potential for incorrect use. If so, then that's one fewer "random" to be confused with one another.
> 
> 
>> 2017/11/24 20:07、Alejandro Alonso <aalonso128 at outlook.com <mailto:aalonso128 at outlook.com>>のメール:
>> 
>> 
>> - Alejandro
>> 
>> ---------- Forwarded message ----------
>> From: Xiaodi Wu <xiaodi.wu at gmail.com <mailto:xiaodi.wu at gmail.com>>
>> Date: Nov 24, 2017, 3:05 PM -0600
>> To: Alejandro Alonso <aalonso128 at outlook.com <mailto:aalonso128 at outlook.com>>
>> Cc: Brent Royal-Gordon <brent at architechies.com <mailto:brent at architechies.com>>, Steve Canon via swift-evolution <swift-evolution at swift.org <mailto: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 <mailto: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 <mailto: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 <mailto:swift-evolution at swift.org>>, wrote:
>>>>> On Fri, Nov 17, 2017 at 7:11 PM, Brent Royal-Gordon <brent at architechies.com <mailto:brent at architechies.com>> wrote:
>>>>>> On Nov 17, 2017, at 3:09 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org <mailto: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 <mailto:swift-evolution at swift.org>
>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution <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 <mailto:swift-evolution at swift.org>>, wrote:
>>> 
>>>> On Fri, Nov 17, 2017 at 7:11 PM, Brent Royal-Gordon <brent at architechies.com <mailto:brent at architechies.com>> wrote:
>>>>> On Nov 17, 2017, at 3:09 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org <mailto: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 <mailto:swift-evolution at swift.org>
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>> 
> 
> 

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