[swift-evolution] [Proposal] Protected Access Level

Vanderlei Martinelli vmartinelli at alecrim.com
Sun May 29 18:50:37 CDT 2016

Hi Leonardo.

Thank you for your answer.

I understand your point of view and I agree that it is better to look
forward. But today we still have to deal with decades of legacy Cocoa code
written using classes. If tomorrow a new set of Cocoa frameworks written in
Swift using protocols appears, maybe we can forget all of this discussion.
But OOP is very important and don't think it is the "past". I see future in
"POP" as I see in "OOP" and I think we can have OOP and POP living in
harmony in Swift. And since we have support to classes in Swift, I think it
shall have a full featured support for classes.

Perhaps my reaction in the last message sounds like I am overreacting when
seen in the context of this thread. But I am programming in Swift since the
first day it was publicly available (and I think that the first almost
usable version to create real world apps was the 1.2). Since the old
forums, when Swift was not yet open source, I have been insisting on
certain improvements.

About bridging member declarations from Objective-C, many of these classes
already have separated headers with the members intended to be overrided.
Exceptions to this rule could be "annotated" somehow. (I would like to
mention classes that are entirely intended to be subclassed and not used as
is in Cocoa frameworks, but this is about "abstract" access level modifier
and not part of this proposal.)


Vanderlei Martinelli

On Sun, May 29, 2016 at 7:45 PM, Leonardo Pessoa <me at lmpessoa.com> wrote:

> Vanderlei, my point in bringing such topics to this discussion is to make
> everyone here think if we're trying to really enhance the language within
> its intended purpose or if we're trying to change the language into
> something else were familiar with from other languages we work/ed with just
> because we're used to work like that. I just started thinking about this
> today and just cannot stop now. No intention to start a war here but I
> think everyone should ask themselves this for every proposed change to the
> language.
> About the topic at-hand, we have to remember Swift is bridged to
> Objective-C, which has no protected (or abstract). How do you propose these
> protected members be bridged should the proposal pass?
> ------------------------------
> From: Vanderlei Martinelli via swift-evolution <swift-evolution at swift.org>
> Sent: ‎29/‎05/‎2016 06:56 PM
> To: swift-evolution <swift-evolution at swift.org>
> Subject: Re: [swift-evolution] [Proposal] Protected Access Level
> Thank you all for your comments. :-)
> Well... My goal is to keep the thing really simple and do not start a new
> "OOP x POP" (or "something" x "other thing") war.
> "Protected" access level is not a new concept at all (except for the Swift
> language), so I did not propose anything preposterous.
> Of course in the Swift of my dreams we also have "abstract" access level
> modifier, "protected" access level, *real* "private" access level and
> "file" access level modifier (along with many, many other things, of
> course). But this proposal is not about this. It is only about include the
> "protected" access level.
> There is, however, something that I need to get off my chest: I really
> would like to have the freedom to go to the depths with protocols as well
> with classes. I work in real apps everyday that uses Cocoa frameworks
> (based on classes) and these apps must be shipped and I like them well
> written. Maybe am I insane for proposing a better support for classes in
> Swift? If so, this explains why every time I suggest better support for
> classes in Swift there is an endless discussion and someone proclaims the
> death of OOP and is it. OK... Maybe someday we will not have more classes
> in Swift. Until there: the current language status is the best way to
> handle OOP in Swift? Or is there a better way? I think there is.
> Regards,
> Vanderlei Martinelli
> On Sat, May 28, 2016 at 7:52 PM, Vanderlei Martinelli <
> vmartinelli at alecrim.com> wrote:
>> Hello.
>> This is the first draft. I'd like to know your opinion about it.
>> (I know that this subject could have been discussed before. If so, please
>> indicate me the correct thread to follow and interact.)
>> Regards,
>> Vanderlei Martinelli
>> ---
>> Introduction
>> Protected access level will enable entities to be used within the
>> container type and by derived types only.
>> Motivation
>> Today Swift has three access levels (public, internal and private), but
>> lacks a way to describe a member that can be only visible to its type or
>> derived types.
>> A common case is the UIView from UIKit. Many developers are tempted to
>> make this call:
>> view.layoutSubviews()
>> The documentation says: "You should not call this method directly. If you
>> want to force a layout update, call the setNeedsLayoutmethod instead to
>> do so prior to the next drawing update. If you want to update the layout of
>> your views immediately, call the layoutIfNeeded method."
>> But yes, you should call this method directly if you are subclassing the
>> view and needs to perform additional layout to its subviews ("subclasses
>> can override this method as needed"):
>> public override func layoutSubviews() {
>>     // We are calling the super method directly here.
>>     super.layoutSubviews()
>>     // Do more adjustments to this view's subviews...}
>> So, yes, we can call this method directly when subclassing, but the Swift
>> compiler will not prevent you from do this when not subclassing or from any
>> other foreign class. It will not even issue a warning.
>> In Objective-C problems like this are usually "solved" my adding a kind
>> of "protected" header (.h) that is intended to be included only when the
>> developer is subclassing. In Swift we do not have headers, but we have the
>> new access level model. So, if the declaration of this method was...
>> protected func layoutSubviews()
>> ... no one outside the class or derived classes would be allowed to call
>> this method directly.
>> Of course, there are other cases in the Cocoa frameworks and there are
>> many other cases when we are developing software in Swift that the
>> protected access level would be very usefull.
>> Proposed solution
>> Create the protected access level.
>> Detailed designReference Types (classes)
>> When declarated by a class the protected member will be visible to the
>> class itself and all the derived classes.
>> // BaseClass.swiftpublic class BaseClass {
>>     public protected(set) var x = 20
>>     protected let y = 10
>>     protected func doSomething() {
>>         // ...
>>     }}
>> // DerivedClass.swiftpublic class DerivedClass: BaseClass {
>>     protected override doSomething() {
>>         self.x = 10 * self.y
>>     }}
>> If the member is declared as final then it will be visible but not can
>> be overrided by the derived classes. Just like it works with other access
>> levels.
>> Value Types (structs, enums, etc.)
>> Value types cannot have derived types. In this case the protected access
>> level does not make sense and will not be allowed in their members.
>> Protocols
>> Protocols do not declare access level for their members. So the protected
> [The entire original message is not included.]
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