[swift-evolution] Proposal: Add Flags to Disable [Optional] Conversions

[Developer]

Oh, definitely.  So, how about a `-Wconversion`-style thing that you can `-Werror` with to get the same effect?  I think this kind of thing satisfies your requirements; It doesn’t create new dialects, is flippable per-file, and doesn’t change the interpretation of valid swift unless the author fully intends to do so.


> On Dec 9, 2015, at 6:10 PM, Chris Lattner <clattner at apple.com> wrote:
> 
> On Dec 9, 2015, at 3:01 PM, Developer <devteam.codafi at gmail.com <mailto:devteam.codafi at gmail.com>> wrote:
>> OK, so Optional conversions need to be re-evaluated, but what about passing a flag disabling all implicit conversions entirely?
> 
> I don’t like the idea of having different incompatible dialects, and behavior changing modes.  That said, I’m personally not opposed to providing functionality that would enable people to use a reduced subsets of the language, and have the compiler enforce it.  For example, I don’t have a problem with someone saying they never want to use the x!, as!, try! family and have the compiler tell them if they do.
> 
> To relate this to your question, I’d be fine with functionality that causes the compiler to produce an error when code requires an implicit conversion, but I wouldn’t want them to be just “disabled”, because I think this could change the interpretation of valid swift code (in admittedly weird cases).
> 
> In terms of how to express this, I’m not in love with modal compiler flags :-).  I’d much rather this sort of requirement be specified as a pragma-like construct that applies to an arbitrary scope (e.g. class or function body) or a whole file.  This keeps the code self describing.
> 
> -Chris
> 
> 
>> 
>>> On Dec 9, 2015, at 5:47 PM, Chris Lattner <clattner at apple.com <mailto:clattner at apple.com>> wrote:
>>> 
>>> 
>>>> On Dec 9, 2015, at 11:20 AM, Developer via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>> 
>>>> Hello all,
>>>> 
>>>> Considering what I do with Swift, I recently posted a pull request that adds a flag to the frontend that would disable all implicit optional conversions by making them errors.  From my perspective, implicit conversions are convenient, but they allow certain strange behaviors (https://github.com/typelift/Swiftz/blob/master/SwiftzTests/EitherSpec.swift#L72 <https://github.com/typelift/Swiftz/blob/master/SwiftzTests/EitherSpec.swift#L72>) to show up.  For the community, the question is threefold:
>>>> 
>>>> 1) Would anything break if this were applied?
>>>> 2) Would it be appropriate to expand the flag by allowing all implicit conversions to be disabled?
>>>> 3) If you remain unconvinced it should be an error, would implicit conversion warnings be more appropriate?
>>> 
>>> Hi Robert,
>>> 
>>> The rules for implicit conversions are optionals need to be re-evaluated, I expect this to happen for Swift 3 (after Swift 2.2 is out of the door).  Once that is done, we can talk about a proposal like this.
>>> 
>>> -Chris
>> 
> 

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