[swift-evolution] [Pitch] New collection-based 'repeat' API

[Xiaodi Wu]

On Mon, May 1, 2017 at 11:22 PM, T.J. Usiyan <griotspeak at gmail.com> wrote:

> Xi: "Does this gain something by being part of the standard library?"
> Me: "This gains discoverability and standardization by being part of the
> standard library."
> Xi: "By definition, if it's in the standard library, it becomes
> standardized and discoverable."
>
> We're in agreement, then?
>

No, you're missing the point entirely. Again, _anything_ gains
"discoverability and standardization" by being included as part of the
standard library. However, the standard library is deliberately small and
is intended to stay that way. So, what should be in and what should be out?
The question is: does this feature gain something by being part of the
standard library which other features that are deliberately excluded (like
left pad) do not?

Repeating a collection endlessly is a useful ability.
>

I don't doubt it. Is your argument that any useful and commonly used
feature should be part of the standard library? That's simply not the
stated criteria for inclusion in the standard library. Hence, why
Foundation exists outside of it. There's no point in debating these
criteria, as (afaict) that's not up for debate. Again, I don't make the
rules. I'm just saying they exist, and I'm arguing that we should abide by
them.


> Yes, it can be written on top of the standard library. It would be
> generally nice not to require that *especially* when we can repeat single
> elements without similar effort. The asymmetry is awkward to remember for
> newbies and awkward to explain away  with "we want a focused library so…
> the Thing A stays but this logically related Thing B can't be in even
> though showing you the ability to do A does tend to lead you to ask after
> Thing B."
>
>
> On Mon, May 1, 2017 at 11:55 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>
>> That's a tautological argument, though. By definition, if it's in the
>> standard library, it becomes standardized and discoverable. This isn't at
>> all a limiting principle for what goes into the library and what doesn't.
>>
>> And as I said, there are many commonly useful facilities that aren't part
>> of the standard library, by design and not by oversight. Left pad is one of
>> them.
>>
>> I'm trying to tease out whether this particular proposal meets the
>> current bar for inclusion. If you believe left pad should be included, your
>> beef is with the deliberate choice to have a small standard library, which
>> as far as I know is not up for reconsideration.
>>
>> On Mon, May 1, 2017 at 22:41 T.J. Usiyan <griotspeak at gmail.com> wrote:
>>
>>> This gains discoverability and standardization by being part of the
>>> standard library. New folks would not have to import some library or roll
>>> their own to get this reasonable to expect/hope or hope for functionality.
>>> Perhaps removing the old function isn't going to work but repeating
>>> collections is definitely something useful.
>>>
>>> Left padding for strings would be nice as well, but that is neither here
>>> nor there.
>>>
>>> On Mon, May 1, 2017 at 11:29 PM, Xiaodi Wu via swift-evolution <
>>> swift-evolution at swift.org> wrote:
>>>
>>>> On Mon, May 1, 2017 at 9:52 PM, Karl Wagner <razielim at gmail.com> wrote:
>>>>
>>>>>
>>>>> > On 2 May 2017, at 04:44, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>>>>> >
>>>>> > Does this gain something by being part of the standard library as
>>>>> opposed to being built on top of it?
>>>>>
>>>>> Well, somebody thought repeatElement<T> was general enough to make
>>>>> part of the standard library. If we’re going to allow repeating a single
>>>>> item as a Collection, we might as well allow generalise it to repeating any
>>>>> Collection in a loop (including a CollectionOfOne, which is the existing
>>>>> use-case).
>>>>>
>>>>
>>>> That doesn't answer the question, though: does the feature you
>>>> propose--repeating any instance of Collection in a loop--gain anything by
>>>> being a part of the standard library rather than an extension to it?
>>>>
>>>> There are _many_ useful algorithms that can be implemented on top of
>>>> the standard library and can be of general use; nonetheless, they aren't a
>>>> part of the standard library. IIUC, it's not because people just haven't
>>>> had the time to flesh it out; rather, it is a deliberate choice to have a
>>>> small, narrowly focused standard library. The philosophy, as I understand
>>>> it, is to make it convenient for users to roll their own conveniences
>>>> rather than providing all the bits and bobs in the library itself.
>>>>
>>>> One of the points of differentiation between standard library and
>>>> Foundation is said to be whether something is necessary to support a core
>>>> language feature, in which case it goes into the standard library. As a
>>>> consequence, there are less commonly used parts of the standard library
>>>> which are there because they support other (decidedly not esoteric) parts
>>>> of the standard library and also happen to have some plausible public uses.
>>>> Taking a quick look into the repository, for instance, `repeatElement` is
>>>> used in the implementation of `UnicodeScalar`. However, just because
>>>> someone determined that `repeatElement` is worth making a public API (since
>>>> it's going to be in the standard library whether or not it's public),
>>>> doesn't _automatically_ mean that a generalization of it should be included
>>>> in the library as well.
>>>>
>>>> Personally, I usually want to repeat a collection of things far more
>>>>> often than I want to repeat an individual thing. It annoys me that the
>>>>> standard library only provides the one I almost never need.
>>>>>
>>>>
>>>> There are many facilities that the standard library does not provide.
>>>> Heck, we don't even have left padding for strings! (JavaScript reference,
>>>> for those following along.) Is there something about this particular
>>>> feature that makes its not being a part of the standard library uniquely
>>>> problematic?
>>>>
>>>> Additionally, it could help remove the top-level “repeatElement”
>>>>> function, which I know irritates some people who would rather us not have
>>>>> any top-level functions in the standard library.
>>>>>
>>>>
>>>> With source stability as a goal, the bar for removal isn't "irritates
>>>> some people." I actively use this function and there's no justification at
>>>> all for breaking it. Frankly, I cannot see removal of top-level functions
>>>> simply because they are top-level to be in scope essentially ever. So let's
>>>> subset that out of this discussion.
>>>>
>>>>
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>>>>
>>>>
>
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