[swift-evolution] Object declarations

[Marc Knaup]

Well anonymous objects are one way object declarations could be used. They
may or may not be reduce clarity - I have no strong preference here.

But they can also be named. This is what interests me most.

Additionally when the compiler knows that there is always exactly one
instance it can probably optimize the code even further.
But I cannot answer that question.

On Mon, Dec 14, 2015 at 1:17 AM, Cole Kurkowski <crk at fastmail.com> wrote:

> I think anonymous classes run counter to Swift's goals of clarity. You
> don't even have to pollute your whole module with the class, you can
> declare a private class in the same file and use it where you need it. This
> is, in my opinion far cleaner. Additionally, anonymous classes are really
> difficult for people to understand if they've not encountered the concept
> before.
>
> On Dec 11, 2015, at 19:48, Marc Knaup via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> @Andrey
>
>    - Note that it should also be possible to create structs anonymously
>    as they also can implement protocols.
>    - Delegates are a bit tricky because they are usually retained weakly
>    so the anonymous object would be deallocated immediately.
>    - Also using "class: XYZ {}" doesn't allow creating named objects like
>    "class object EmptyObject {}".
>
> When talking about singletons people tend to first think at a very large
> scale and about abstraction, factories, testability and whatever.
> It's the little things which capture my interest more, like NSNull for
> example.
>
> class object NSNull {}
>
> Or maybe a JSON Null:
>
> protocol JSONNode {}
> struct JSON {
>     struct object Null: JSONNode {}
>     struct Bool { … } // not an object but a type
>
>     // …
> }
>
> Now the interesting part about a singleton NSNull (or the JSON one) is
> that it represents both, a type and an instance.
>
> array.append(NSNull)
>
> Note that we cannot use a class and call NSNull() as this would create a
> new instance instead of returning the singleton instance.
> We would have to make a silly workaround like NSNull.null or
> NSNull.sharedInstance.
>
> Examples for JSON.Null:
>
> jsonArray.append(JSON.Null) // used as instance
>
> if jsonNode is JSON.Null { // used as type
>    // …
> }
>
> let expectedJsonTypes: [JSONNode.Type] = [JSON.Null, JSON.Bool, …]
>
> if jsonNode is JSON.Null { // used as type
>    // …
> }
> if jsonNode == JSON.Null { // used as instance (assuming Equatable
> conformance)
>    // …
> }
>
>
>
>
>
>
> On Sat, Dec 12, 2015 at 2:29 AM, Andrey Tarantsov via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> I think that anonymous classes got lost amongst all the singletonphobia
>> here, and yet making an anonymous local delegate class is often helpful.
>>
>> Perhaps we don't need an additional keyword, though; something like this
>> could work too:
>>
>> view.delegate = class: SomeDelegate {
>>   ...
>> }()
>>
>> or perhaps you want a slightly customized object:
>>
>> view = class: UITextField {
>>   func canBecomeFirstResponder() -> Bool { return false }
>> }()
>>
>> Of course, we could just use a named local class, like others have
>> pointed out, but unless you really want to name that thing (and the name
>> would often be stupid), that's a just workaround for a lack of anonymous
>> classes.
>>
>> A.
>>
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