[swift-evolution] My personal beef with leading-dot syntax

[Joe Groff]

> On Apr 4, 2016, at 12:51 PM, Dave Abrahams <dabrahams at apple.com> wrote:
> 
> 
> on Mon Apr 04 2016, Joe Groff <jgroff-AT-apple.com> wrote:
> 
>>> On Apr 4, 2016, at 11:44 AM, Dave Abrahams <dabrahams at apple.com> wrote:
>>> 
>>> 
>>> on Mon Apr 04 2016, Joe Groff <jgroff-AT-apple.com> wrote:
>>> 
>> 
>>>>> On Apr 4, 2016, at 11:05 AM, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
>>>>> 
>>>>> 
>>>>> on Mon Apr 04 2016, Erica Sadun <swift-evolution at swift.org> asked:
>>>>> 
>>>> 
>>>>>> Can you ping me off-list or in another thread and explain what the
>>>>>> issues are?
>>>>> 
>>>>> All of the following make me uncomfortable with our leading-dot thang:
>>>>> 
>>>>> * The rules for lookup don't seem obvious to me.  I admit this is very
>>>>> personal/subjective.
>>>>> 
>>>>> * There is some evidence that people think it means something it doesn't
>>>>> (“enum case”), as mentioned in SE-0036.  That suggests it is a
>>>>> confusing feature.  That confusion may be fairly harmless so far, but
>>>>> still.
>>>>> 
>>>>> * The dot doesn't seem to buy enough to be worth the complexity it adds
>>>>> to the language; why not just let those names be looked up without the
>>>>> dot?  You can always disambiguate with full qualification if you have
>>>>> to.
>>>> 
>>>> Making every unqualified reference context-dependent would be
>>>> impractical. `foo.bar(bas)` would become an exponential search to find
>>>> a contextual type containing a `foo` which has a `bar` member that can
>>>> accept an type containing a `bas` member.
>>> 
>>> I don't think I'm talking about making every unqualified reference
>>> context-dependent.  When I have a context that demands an instance of a
>>> particular enum type, I think it's reasonable to look up the names in
>>> the enum without qualification, and I strongly question the value of
>>> leading-dot syntax for general static member lookup.
>> 
>> Therein lies the rub—*any* context an unqualified name can appear in
>> could potentially demand an instance of a particular enum type, until
>> the type checker rules that out. Limiting the behavior to enums
>> doesn't simplify the implementation.
> 
> I'm afraid I don't understand how that's a serious problem yet.

Right now, we limit the contextual lookup to places where it's syntactically asked for, using the leading dot. Without the leading dot, we'd have to extend it to every unqualified name, which makes it much more likely you'll fall into problematic cases.

-Joe