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

[Evan Maloney]

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> 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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> 

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