I don’t understand how
ApiClient().fetchUsers().then(#set(users))
leads to
ApiClient().fetchUsers().then(displayUsers)
Could you clarify with a more extensive example?
What does the function then() do?
-Kenny
> On Jun 28, 2016, at 11:18 AM, Austin Feight via swift-evolution
> <[email protected]> wrote:
>
> Proposal:
>
> I propose adding setter methods to vars, which could look something like
> this: `ApiClient().fetchUsers().then(#set(users))`
>
> Initially I thought it should work like this:
> `ApiClient().fetchUsers().then(users.set)`
> but to accomplish a line of code that flows grammatically, I believe putting
> "set" where it would naturally fall if the code was being read as a sentence
> is more Swifty.
>
> Rationale:
>
> The following code makes me smile:
>
> ApiClient().fetchUsers().then(displayUsers)
>
> It exemplifies the beauty of Swift. First-class functions make this line of
> code read very well. Consider some alternatives:
>
> 1. ApiClient().fetchUsers().then { displayUsers($0) }
> 2. ApiClient().fetchUsers().then { users in displayUsers(users) }
> 3. ApiClient().fetchUsers().then { (users: [User]) in displayUsers(users) }
>
> Using the lessons learned from Swift API Design Guidelines (WWDC 2016 Session
> 403) having an emphasis on clarity, my analysis of the alternatives is:
>
> 1. $0 adds no additional information as to the type or explanation of what
> the argument is, thus adding nothing to the line of code for clarity, and
> therefore should be omitted
> 2. adding "users" also adds nothing to the clarity of the code. The function,
> properly, contains the information necessary to reason about the argument it
> takes and what it does, and therefore adding "users" is redundant
> 3. Not only is "users" redundant, but also is the explicit type label. The
> `displayUsers` method will only accept one type of argument, so we're
> duplicating information that the compiler (and autocomplete) already gives us
>
> With this I conclude that `ApiClient().fetchUsers().then(displayUsers)` is
> the Swiftiest option.
> I want to extend this same logic to when I find myself writing code like this:
>
> ApiClient().fetchUsers().then { users in
> self.users = users
> }
>
> or alternatively, because "users" is likely redundant information again,
>
> ApiClient().fetchUsers().then { self.users = $0 }
>
> Personally I steer clear of `$0` as much as possible, because I very rarely
> feel that it provides the information necessary for code clarity. But beyond
> that, this code no longer reads as nicely as the code we had before.
>
> Whereas `ApiClient().fetchUsers().then(displayUsers)` flows nicely as a
> sentence and reads grammatically, `ApiClient().fetchUsers().then { self.users
> = $0 }` no longer does.
>
> I think this feature could have a simple implementation where the compiler
> replaces `#set(X)` with `{ X = $0 }`, and I believe it would go a long way
> with respect to code clarity, especially when X is something longer like
> `self.view.bounds.origin.x`
>
>
> Looking forward to hearing thoughts from the community,
> Austin Feight
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