> On Mar 21, 2017, at 11:00 AM, Colin Barrett via swift-evolution > <swift-evolution@swift.org> wrote: > > > > On Thu, Mar 16, 2017 at 3:33 PM Itai Ferber via swift-evolution > <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: > > Here's what I mean: Suppose I have a BlogPost model, and I can both fetch and > post BlogPosts to a cross-platform web service, and store them locally. But > when I fetch and post remotely, I ned to conform to the web service's > formats; when I store an instance locally, I have a freer hand in designing > my storage, and perhaps need to store some extra metadata. How do you imagine > handling that sort of situation? Is the answer simply that I should use two > different types? > > This is a valid concern, and one that should likely be addressed. > > Perhaps the solution is to offer a userInfo : [UserInfoKey : Any] > (UserInfoKey being a String-RawRepresentable struct or similar) on Encoder > and Decoder set at the top-level to allow passing this type of contextual > information from the top level down. > > > I assumed that in those situations, one would create a wrapper struct, > > struct WebBlogModel { > let wrapped: BlogModel > } > > probably for the encoding impl that requires more custom work. The > implementation of Codable for this struct would then serialize (deserialize) > from (to) its wrapped value's properties directly. > > Types already provide a means for performing context sensitive implementation > selection, I don't think it's necessary to provide another way to do that in > Swift. Of course I could very well be wrong :)
Wrappers like this give you a way to implement different encoding strategies but they don’t help you identify which strategy to use for a given encoding. You need a user-defined context to do that. Brent has proposed a couple of different designs to facilitate this which are nicer than a user info dictionary. > > -Colin > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution
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