[swift-evolution] [Proposal] Random Unification
xiaodi.wu at gmail.com
Sun Nov 5 19:56:00 CST 2017
I like this particular version. In particular, the choice of algorithms is,
afaict, correct and that is incredibly important. I had overlooked that
`arc4random` is cryptographically secure past a certain version of macOS,
but you are absolutely right. I am also on board with the fatal error
suggestion if random entropy is unavailable; I think it must be amply
I do think, however, that you're overloading too many things into the word
"random" when they're not the same. Take a look at Python, which is pretty
widely used for numerics. There's `rand` and `random` for getting a random
integer or floating-point value, and there's `choice` and `sample` for
choosing one or more values out of a collection without replacement. These
are sufficiently different tasks and don't all need to be called "random"
or satisfy the same requirement of the same protocol. Put another way, it's
absolutely *not* inconsistent for numeric types to have `random()` while
collection types have a differently named method.
By contrast, I think the great length of text trying to justify naming all
of these facilities `random` in order to parallel `first` and `last` shows
how the proposed design is comparatively weaker. You have to argue that (a)
`Int.random` shouldn't return an optional value because it'd be unwieldy,
and therefore `(0..<5).random` shouldn't either because it would then be
inconsistent; but (b) that `(0..<5).random` should be spelled and behave
like `(0..<5).first` and `(0..<5).last` even though the user must handle
empty collections totally differently because the return types are not the
same. Either `(0..<5).random` should behave analogously to `first` and
`last` or it should not. If it should, it only makes sense to return a
result of type `T?`. After all, if a collection doesn't have a `first`
item, then it can't have a `random` item. Put another way, having a `first`
item is a prerequisite to having a randomly selectable item. The behavior
of the Swift APIs would be very consistent if `first` returns `T?` but
`random` returns `T`. However, I agree that unwrapping `Int.random` every
time would be burdensome, and it would not make sense to have a type
support `random` but not have any instantiable values; therefore, returning
an optional value doesn't make sense, and it follows that `Int.random`
*shouldn't* behave like `first` or `last`.
Once you stop trying to make what Python calls `rand/randint` and
`choice/sample` have the same names, then finding a Swifty design for the
distinct facilities becomes much easier, and it suggests a pretty elegant
[1, 2, 3, 4].choice // like `first` or `last`, this gets you a value of
[1, 2, 3, 4].sampling(2) // like `prefix(2)` or `suffix(2)`, this gets you
a subsequence with at most two elements
Int.random // this gets you a random Int; or it may trap
Float.random // this gets you a random Float; or it may trap
With that, it also becomes clear why--and I agree with you--an independent
`Int.random(in: 0..<5)` is not necessary. `(0..<5).choice` is fine, and it
can now appropriately return a value of type `T?` because it no longer
needs to parallel `Int.random`.
* * *
More in the bikeshedding arena, I take issue with some of the names:
- I reiterate my comment that `Randomizable` is not the best name. There
are multiple dictionary definitions of "randomize" and one is "make
unpredictable, unsystematic, or random in order or arrangement." Wikipedia
gives at least five different contextual meanings for the word. What you're
doing here is specifically **random sampling** and we can do better to
clarify that, I think.
- While I agree that `RNG` can be cryptic, the alternative should be
`RandomNumberGenerator` (as it's called in other languages);
`RandomGenerator` is not quite accurate. Again, we're _consuming_
randomness to _generate_ numbers (or values of other type, based on the
result of a generated number). We're not _generating_ randomness.
On Sun, Nov 5, 2017 at 6:33 PM, Alejandro Alonso <aalonso128 at outlook.com>
> https://github.com/apple/swift-evolution/pull/760 is the current API and
> proposed solution.
> - Alejandro
> On Nov 5, 2017, 6:18 PM -0600, Xiaodi Wu <xiaodi.wu at gmail.com>, wrote:
> My comments are directed to the "more up-to-date" document that you just
> linked to in your reply to Jon. Is that one outdated? If so, can you send a
> link to the updated proposal and implementation for which you're soliciting
> On Sun, Nov 5, 2017 at 6:12 PM, Alejandro Alonso <aalonso128 at outlook.com>
>> The proposal and implementation have the current updated API. The link I
>> sent Jon was the one I brought up a few weeks ago which is outdated now.
>> The proposal answers all of your questions. As for `.random` being a
>> function, some would argue that it behaves in the same way as `.first` and
>> `.last` which are properties.
>> - Alejandro
>> On Nov 5, 2017, 6:07 PM -0600, Xiaodi Wu <xiaodi.wu at gmail.com>, wrote:
>> A few quick thoughts:
>> I know that there's been some discussion that `(1...10).random` is the
>> best spelling, but I'd like to push back on that suggestion. When I want a
>> random number, I tend to think of the type I want first ("I want a random
>> integer") and then a range ("I want a random integer between a and b"), not
>> the other way around. My intuition is that `Int.random(in:)` will be more
>> discoverable, both on that basis and because it is more similar to other
>> example). It also has the advantage that the type is explicit, which I
>> think is particularly useful in this case because the value itself is,
>> well, random.
>> I would also argue that, `random` is most appropriately a method and not
>> a property; there's no hard and fast rule for this, but the fact that the
>> result is stochastic suggests (to me) that it's not a "property" of the
>> range (or, for that matter, of the type).
>> I would reiterate here my qualms about `Source` being the term used for a
>> generator. These types are not a _source_ of entropy but rather a
>> _consumer_ of entropy.
>> `UnsafeRandomSource` needs to be renamed; "unsafe" has a specific meaning
>> in Swift--that is, memory safety, and this is not it. Moreover, it's
>> questionable whether this protocol is useful in any sense. What useful
>> generic algorithms can one write with such a protocol?
>> `XoroshiroRandom` cannot be seeded by any `Numeric` value; depending on
>> the specific algorithm it needs a seed of a specific bit width. If you
>> default the shared instance to being seeded with an `Int` then you will
>> have to have distinct implementations for 32-bit and 64-bit platforms. This
>> is unadvisable. On that note, your `UnsafeRandomSource` needs to have an
>> associated type and not a generic `<T : Numeric>` for the seed.
>> The default random number generator should be cryptographically secure;
>> however, it's not clear to me that it should be device random.
>> I agree with others that alternative random number generators other than
>> the default RNG (and, if not default, possibly also the device RNG) should
>> be accommodated by the protocol hierarchy but not necessarily supplied in
>> the stdlib.
>> The term `Randomizable` means something specific which is not how it's
>> used in your proposed protocol.
>> There's still the open question, not answered, about how requesting an
>> instance of the hardware RNG behaves when there's insufficient or no
>> entropy. Does it return nil, throw, trap, or wait? The proposed API does
>> not clarify this point, although based on the method signature it cannot
>> return nil or throw. Trapping might be acceptable but I'd be interested to
>> hear your take as to why it is preferable.
>> On Sun, Nov 5, 2017 at 4:43 PM, Alejandro Alonso via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>> For the proof of concept, I had accidentally deleted that one. I have a
>>> more up to date one which was discussed a few weeks later.
>>> - Alejandro
>>> On Nov 5, 2017, 4:37 PM -0600, Jonathan Hull <jhull at gbis.com>, wrote:
>>> Is there a link to the writeup? The one in the quote 404s.
>>> On Nov 5, 2017, at 2:10 PM, Alejandro Alonso via swift-evolution <
>>> swift-evolution at swift.org> wrote:
>>> Hello once again Swift evolution community. I have taken the time to
>>> write up the proposal for this thread, and have provided an implementation
>>> for it as well. I hope to once again get good feedback on the overall
>>> - Alejandro
>>> On Sep 8, 2017, 11:52 AM -0500, Alejandro Alonso via swift-evolution <
>>> swift-evolution at swift.org>, wrote:
>>> Hello swift evolution, I would like to propose a unified approach to
>>> `random()` in Swift. I have a simple implementation here
>>> https://gist.github.com/Azoy/5d294148c8b97d20b96ee64f434bb4f5. This
>>> implementation is a simple wrapper over existing random functions so
>>> existing code bases will not be affected. Also, this approach introduces a
>>> new random feature for Linux users that give them access to upper bounds,
>>> as well as a lower bound for both Glibc and Darwin users. This change would
>>> be implemented within Foundation.
>>> I believe this simple change could have a very positive impact on new
>>> developers learning Swift and experienced developers being able to write
>>> single random declarations.
>>> I’d like to hear about your ideas on this proposal, or any
>>> implementation changes if need be.
>>> - Alejando
>>> swift-evolution mailing list
>>> swift-evolution at swift.org
>>> swift-evolution mailing list
>>> swift-evolution at swift.org
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