If we're to introduce the protected visibility, I think we should as well make
it automatically internal or introduce an explicit protected internal
visibility. I've been through many cases while programming in C# 'where' this
was handy (thou I cannot name one from memory right now; it's been so many
years ago...)
-----Original Message-----
From: "Xiaodi Wu via swift-evolution" <[email protected]>
Sent: 28/05/2016 08:10 PM
To: "Vanderlei Martinelli" <[email protected]>; "swift-evolution"
<[email protected]>
Subject: Re: [swift-evolution] [Proposal] Protected Access Level
Seems entirely reasonable to me. POP aficionados may object, but I think the
pros and cons of this type of access are well trodden terrain and I think it's
a net win to have this available in Swift going forward.
On Sat, May 28, 2016 at 18:53 Vanderlei Martinelli via swift-evolution
<[email protected]> 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 design
Reference Types (classes)
When declarated by a class the protected member will be visible to the class
itself and all the derived classes.
// BaseClass.swift
public class BaseClass {
public protected(set) var x = 20
protected let y = 10
protected func doSomething() {
// ...
}
}
// DerivedClass.swift
public 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
access level is not applicable here.
Extensions
Extensions will not be able do be protected nor their members.
Special Note
The protected access level can only be applied to classes, structs and other
types when nested inside other type. So the following code will not compile:
<code
style="margin:0px;padding:0px;border:none;border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;background-image:none;font-family:Consolas,Monaco,'Andale
Mono
[The entire original message is not included.]_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
