> On 15 Jun 2017, at 19:28, Chris Lattner <[email protected]> wrote:
>
>
> On Jun 15, 2017, at 9:41 AM, Xiaodi Wu via swift-evolution
> <[email protected] <mailto:[email protected]>> o
>>> >
>>> > let (a : Int, b : Float) = foo()
>>>
>>>
>>> I think it would be better if the compiler raised a warning whenever you
>>> tried to redefine a builtin type.
>>>
>>> That’s essentially my preferred solution as well, as it gets to the root of
>>> the confusion.
>>>
>>> Naming a variable the same as a type should be similar to naming a variable
>>> the same as a reserved keyword and require backticks. (A previous
>>> suggestion to enforce capitalization falls down with full Unicode support
>>> and complicates interop where imported C structures might be lowercase and
>>> constants might be all caps.) No need to treat built-in types specially;
>>> it’s equally a problem with types imported from other libraries, which can
>>> be shadowed freely today. For full source compatibility this can be a
>>> warning instead of an error–should be sufficient as long as it’s brought to
>>> the user’s attention. In fact, probably most appropriate as a warning,
>>> since the _compiler_ knows exactly what’s going on, it’s the human that
>>> might be confused.
>>
>> I kind of agree with all you say. But I also feel that tuple element names
>> in patterns are very rarely used and not worth the added complexity and
>> confusing. Going back to the old: “Would be add it to Swift if it did not
>> exist?”, I would say no.
>>
>> That was the standard for removing features before Swift 3, but with source
>> compatibility the bar is now much higher.
>
> Completely agreed. My belief on this is that it is a legacy Swift 1 type
> system capability that no one uses. I have no data to show that though.
>
>> Is the feature harmful?
>
> Yes, absolutely. The shadowing isn't the thing that bothers me, it is that
> swift has a meaning for that very syntax in other contexts, and that this is
> completely different meaning. People absolutely would get confused by this
> if they encountered it in real code that they themselves didn't write, and
> I'm not aware of any good (non theoretical) use for it.
>
>> My point is, not on its own it isn’t: warning on variables shadowing types
>> is sufficient to resolve the problems shown here.
>
> Again, my concern is that this is a confusing and misleading feature which
> complicates and potentially prevents composing other features in the future.
>
>
>>
>> How strange that we’re talking about this issue in a thread about SE-0110.
>
> This came up in the discussion about 110 because we were exploring whether it
> was plausible to expand the function parameter grammar to support
> destructuring in the position where a name goes. There are many concerns
> about whether this is a good idea, but he existence of this in the tuple
> destructuring pattern grammar is pretty much a showstopper.
>
>> If anything, the response to that proposal should be a cautionary tale that
>> users can take poorly to removing features, sometimes in unanticipated ways.
>
> Agreed, it may be too late to correct this (certainly we can't outright
> remove it in Swift 4 if someone is using it for something important).
> However if it turns out that it really isn't used, then warning about it in 4
> and removing it shortly after may be possible.
And I think its difficult to make the parallel between the two. SE-0110
basically impacted everybody calling higher-order functions on Dictionary (+
more users from libraries like RxSwift), which makes an enormous proportion of
the Swift community. On the other hand, despite the enormous amount of time I
have sinked into learning, discussing and enjoying Swift, I never come upon the
tuple element name syntax in patterns until Robert pointed to it out on twitter
several weeks ago.
> -Chris
>
>>
>>> `let (a : Int, b : Float) = foo()` is confusing but if you were to use your
>>> own type (e.g., `struct S {}` and replace Int and Float with S) you would
>>> get a compiler error. If the compiler warned you that you were reassigning
>>> Int and Float, you’d probably avoid that problem. Or, for a more extreme
>>> fix, we could make reassigning builtin types illegal since there is pretty
>>> much no valid reason to do that.
>>>
>>>
>>> > On Jun 15, 2017, at 8:10 AM, Matthew Johnson via swift-evolution
>>> > <[email protected] <mailto:[email protected]>> wrote:
>>> >
>>> >
>>> >
>>> > Sent from my iPad
>>> >
>>> >> On Jun 14, 2017, at 11:01 PM, Chris Lattner via swift-evolution
>>> >> <[email protected] <mailto:[email protected]>> wrote:
>>> >>
>>> >>
>>> >>> On Jun 12, 2017, at 10:07 PM, Paul Cantrell <[email protected]
>>> >>> <mailto:[email protected]>> wrote:
>>> >>>
>>> >>> What’s the status of this Chris’s double parens idea below? It garnered
>>> >>> some positive responses, but the discussion seems to have fizzled out.
>>> >>> Is there something needed to help nudge this along?
>>> >>>
>>> >>> What’s the likelihood of getting this fixed before Swift 4 goes live,
>>> >>> and the great wave of readability regressions hits?
>>> >>
>>> >> We discussed this in the core team meeting today. Consensus seems to be
>>> >> that a change needs to be made to regain syntactic convenience here.
>>> >> Discussion was leaning towards allowing (at least) the parenthesized
>>> >> form, but more discussion is needed.
>>> >>
>>> >>
>>> >> One (tangential) thing that came up is that tuple element names in tuple
>>> >> *patterns* should probably be deprecated and removed at some point.
>>> >> Without looking, what variables does this declare?:
>>> >>
>>> >> let (a : Int, b : Float) = foo()
>>> >
>>> > Another option would be to require let to appear next to each name
>>> > binding instead of allowing a single let for the whole pattern. I
>>> > personally find that much more clear despite it being a little bit more
>>> > verbose.
>>> >
>>> >>
>>> >> ?
>>> >>
>>> >> -Chris
>>> >>
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