[swift-users] Possible compiler bug? Unable to extend a type whose name clashes

[Jordan Rose]

Sure, go ahead. (The associated Radar also deals with a non-generic type; sorry I didn't include that in the SR.)

Jordan


> On Mar 9, 2016, at 8:23 , Evan Maloney <emaloney at gilt.com> wrote:
> 
> Thanks a lot, Jordan; your suspicion is correct! That appears to be the issue I'm having--although unlike what's captured in the JIRA ticket, in my case there are no generics involved.
> 
> Would you mind if I updated this ticket with the additional info related to the scenario I hit?
> 
> 
> 
>> On Mar 8, 2016, at 5:41 PM, Jordan Rose <jordan_rose at apple.com <mailto:jordan_rose at apple.com>> wrote:
>> 
>> Hi, Evan. Just a suspicion: do you also have a type named AppleTart? In that case you'd be hitting SR-898 <https://bugs.swift.org/browse/SR-898>, rather than a specific issue with extensions.
>> 
>> Jordan
>> 
>> 
>>> On Mar 8, 2016, at 14:26, Evan Maloney via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>>> 
>>> I recently ran into a situation where I needed to import a symbol with the same name from two different modules, and noticed that the usual Swift technique of disambiguating using the package name doesn't work when used with extensions.
>>> 
>>> In my case, I have a package 'LegacyStore' and a package 'AppleTart', both of which contain a type named 'User'.
>>> 
>>> In the case of LegacyStore, User is an Objective-C class, and in the case of AppleTart, User is a Swift struct.
>>> 
>>> Normally, I'd be able to refer to one as 'LegacyStore.User' and the other as 'AppleTart.User', but when using this notation for an extension:
>>> 
>>>    extension AppleTart.User
>>>    {
>>>        public var legacyUser: LegacyStore.User {
>>>            // implementation
>>>        }
>>>    }
>>> 
>>> ...I get a compiler error on the extension declaration line:
>>> 
>>>    error: 'User' is not a member type of 'AppleTart'
>>> 
>>> Note that the 'LegacyStore.User' notation used in the var declaration never triggers a compiler error, so I'm assuming the notation just isn't supported yet in the context of declaring an extension.
>>> 
>>> Fortunately, there's a (somewhat cumbersome) work-around, which is to create two separate files, one for each module. Within each file import just that one module, and create a typealias for each clashing name using package-qualified name of the type.
>>> 
>>> For example, here's the relevant part of my AppleTartTypeDisambiguation.swift file:
>>> 
>>>    import AppleTart
>>> 
>>>    public typealias AppleTartUser = User
>>> 
>>> And here's my LegacyStoreTypeDisambiguation.swift file:
>>> 
>>>    import LegacyStore
>>> 
>>>    public typealias LegacyUser = User
>>> 
>>> I can then use the typealiases to extend either type. For example, here's how I successfully extended AppleTart.User:
>>> 
>>>    extension AppleTartUser
>>>    {
>>>        public var legacyUser: LegacyStore.User {
>>>            // implementation
>>>        }
>>>    }
>>> 
>>> Should the inability to extend a type using the qualified type name be considered a compiler bug? I'm assuming yes. If so, I'll file a ticket.
>>> 
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>>> swift-users at swift.org <mailto:swift-users at swift.org>
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>> 
> 

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