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

[Jordan Rose]

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> 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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