+1 :)
Let’s analyze this: public > internal > fileprivate >= private
An extension may optionally be marked with an explicit access modifier that
specifies the default scope [see SE–0025]. However, such an explicit modifier
must not match (or exceed) the original type’s access level.
public struct A {}
// I assume that we go with "must not match" here!
// can't be public anymore -> no more
// <<implicitly>> public extension members
// -> breaking change -> I can live with that
extension A {}
// no default access modifier -> extension
// follows the access rule by the extended type A
// -> here every extension member is internal by default
// -> can be overridden to public member wise
extension A {}
// default access modifier acts as the upper bound
// inside an extended public type A
// -> every extension member are fileprivate
// -> extension member can be explicitly set to private
// -> these will be only visible inside this extension scope
fileprivate extension A {}
// at file scope `private` acts like `fileprivate`
// (if `private` is allowed at filescope) - haven't read the extended SE-0025
yet
// -> I assume any member that are explicitly set to private
// will only be visible inside this extension scope
private extension A {}
Let’s check internal types:
internal struct B {}
// "must not match" does not work here anymore
// do we use "must not exceed" here???
// I assume the second.
// doens't break anything
// works as before
// no default access modifier for internal types
// equals `internal extension A {}`
// members are default internal
// -> can be overridden to `fileprivate` or scope level `private`
extension B {}
// same as for `public extension A`
fileprivate extension B {}
// same as for `public extension A`
private extension B {}
// that sounds fine right?
// let's check if we'd go with "must not match" instead:
// we cannot extend internal types with internal members
// anymore -> ups, that would be really strange
extension B {}
// same as for `public extension A`
fileprivate extension B {}
// same as for `public extension A`
private extension B {}
Just for the record we also check fileprivate and private:
fileprivate struct C {}
// "must not exceed" assumed
// no default access modifier means all
// extension member will folow the upper bound by
// the extended type -> fileprivate by default
// -> members can be set to be `private` and only
// visible inside this extension scope
// -> equivalent to `fileprivate extension B {}`
// and `private extension C {}`
extension C {}
// "must not match" -> would break like it breaks the
// internal access model
``swift // at file scope acts likefileprivate` private struct D {}
// “must not exceed” assumed
// same as for fileprivate extension D {}
// “must not match” -> would break ```
Great compromise here!
This rule would preserve the possibility of using extensions as grouping
constructs. At the same time, it would (1) remove the possibility of writing
public extension to default the access level of members to public;
We still can group internal and fileprivate with this, but it’s okay I guess.
Let’s re-check default protocol implementation:
public protocol G {
func foo()
}
// currently we have 3 different ways to make them public
// #1
extension G {
public func foo() { /* implement */ }
}
// #2
public extension G {
func foo() { /* implement */ }
}
// #3
public extension G {
public func foo() { /* implement */ }
}
// with "must not match" for `public` only #1 will work
// but everyone will need to repeat `public`
// no laziness for `public` anymore - hurray
extension G {
public func foo() { /* implement */ }
}
// "must not exceed" doesn't solve the problem of `public` at all
The last topic is conformance to protocols:
public protocol P {}
internal protocol PI {}
fileprivate protocol PF {}
private protocol PP {}
public type Y {}
// "must not exceed" results in this, which is what it looks right now
extension Y : P {}
// just fine here
// we still can grant `PI` members visibility up to `public`
// the lower bound for these is `internal`
extension Y : PI {}
// same as `PI` but the lower bound is `fileprivate` now
extension Y : PF {}
// same as `PI` but the lower bound is `private` now
extension Y : PP {}
// this does not work atm.
// but should be allowed in general where we could grant visibility up to
`internal`
internal extension Y : PI, PF, PP {}
fileprivate extension Y : PF, PP {}
There are a few more combinations I don’t want to type out here.
My conclusion it this:
“must not match” does solve a few problems with public but only allows explicit
internal, fileprivate and private usage, which is kinda odd. This is a new
exceptional rule that must be documented.
“must not exceed” does not solve anything if it does not follow the typical
public with default internal rule.
With this exception it’s no more a default access modifier and totally useless
on extensions, except if >>no access modifier<< would mean the upper bound is
implicitly internal where you can’t grant visibility up to public and forced to
use public extension if you wish to achieve this.
With the exception in (1) we would need to allow access modifier on extension
with protocol conformance to achieve the same result everywhere.
With all that we’ll have to use #3 for default protocol implementations to make
them public.
That said we’re end up with the same upper- lower bound access control model on
extension I proposed, even if my proposal title and some of my writing there
caused a lot of confusion.
--
Adrian Zubarev
Sent with Airmail
Am 18. Juli 2016 um 11:14:09, David Hart ([email protected]) schrieb:
This compromise solution looks very good to me. Thanks Xiaodi for the effort
put into working through our whining to come to the best solution IMHO.
On 18 Jul 2016, at 09:50, Xiaodi Wu via swift-evolution
<[email protected]> wrote:
All righty, thanks for all of your feedback. I've worked on revising the
proposal this evening, re-reading previous documents and messages and
re-analyzing what people meant. I think Jose is absolutely right in the end,
and the proposal has turned out like he suggested. Here is the current draft
below:
Harmonize access modifiers for extensions
Proposal: SE-XXXX
Author: Xiaodi Wu
Status: Awaiting review
Review manager: TBD
Introduction
During discussion of SE-0119, some voiced concern that writing public extension
increases the default access level for members declared within that extension,
whereas writing public class or public struct does not do the same.
This behavior is explained as follows: since extensions have no runtime
representation and are not first-class entities, access modifiers on extensions
serve as a shorthand to set the default access level for members. Certain
members of the community have indicated that such behavior makes extensions a
natural grouping construct.
A general principle of Swift, recently strengthened by proposals such as
SE-0117, has been that public API commitments should require explicit opt-in.
Given the different behavior of classes and structs, the fact that extensions
allow public methods to be declared without spelling out public at the
declaration site has been called "confusing" or "odd."
The aim of this proposal is to, in as conservative a manner as possible,
require explicit use of public for public methods declared inside any extension.
Swift-evolution threads:
[Proposal] Revising access modifiers on extensions
[Review] SE-0119: Remove access modifiers from extensions
[Draft] Harmonize access modifiers for extensions
Motivation
Consider the following:
public struct foo {
func frobnicate() { } // internal
}
public extension foo { }
public struct bar { }
public extension bar {
func frobnicate() { } // public
}
This outcome is explained by rules regarding access modifiers specifically on
extensions Swift 2, which is slated for preservation in Swift 3 as detailed in
SE-0025. However, it is arguably surprising that, of two declarations spelled
identically, one leads to a public API commitment while the other does not.
Proposed solution
The proposed solution is to amend access modifier rules to eliminate the
possibility of defaulting the access level of members declared inside an
extension to public.
Detailed design
Amend access modifier rules as follows:
An extension may optionally be marked with an explicit access modifier that
specifies the default scope [see SE-0025]. However, such an explicit modifier
must not match (or exceed) the original type's access level.
This rule would preserve the possibility of using extensions as grouping
constructs. At the same time, it would (1) remove the possibility of writing
public extension to default the access level of members to public; and (2)
clarify the notion that an access modifier on an extension is a shorthand and
not a way to create a first-class entity by disallowing repeating of the
original type's access level.
Explicit access modifiers will continue to set the maximum allowed access
within an extension, as clarified in SE-0025.
Alternatives considered
One alternative is to eliminate explicit access modifiers on extensions
altogether. As an advantage, this would further clarify the mental model that
extensions are not their own first-class entities. As a disadvantage,
extensions cease to be an access modifier grouping construct, which some users
really like.
Acknowledgments
Thanks to all discussants on the list, especially Adrian Zubarev, Jose Cheyo
Jimenez, and Paul Cantrell.
On Sun, Jul 17, 2016 at 11:08 AM, Xiaodi Wu <[email protected]> wrote:
I understand how it works.
By aligning access modifier rules inside extensions with those inside types,
all other modifiers would continue to work as it does now (implicitly internal
members would be limited by the upper bound). The only change in this respect
is removing the ability to have public API without writing `public func`.
On Sun, Jul 17, 2016 at 11:01 Adrian Zubarev via swift-evolution
<[email protected]> wrote:
I tackled it as an upper bound but highly rejected by the community. That’s
exactly what my proposal was all about. An upper boundary would be more
elegant, but I still see arguments ‘because it’s not a type’.
I could live without access modifiers on extensions in general.
The default access modifier rule permits public methods to be written without
public func
You meant this?
public extension SomeType {
// I don't need to write public
func foo() {}
var computed: Type {}
}
This applies to all access modifiers which are not optional (like internal):
public SomeType
fileprivate extension SomeType {
// I don't need to repeat fileprivate
func foo() {}
var computed: Type {}
}
// which is more likely `fileprivate` because it's on file scope
private extension SomeType {
// even if the inner access modifier would pretend to be private
// since the extension is on filescope, everything will be `fileprivate`
func foo() {}
var computed: Type {}
}
--
Adrian Zubarev
Sent with Airmail
Am 17. Juli 2016 um 17:50:31, Xiaodi Wu ([email protected]) schrieb:
The proposal is that the access modifier for an extension will either be
removed entirely or remain as an upper bound, losing its function as a default
access modifier. The default access modifier rule permits public methods to be
written without `public func`; this is a proposal to remove that feature
because it is a source of confusion.
On Sun, Jul 17, 2016 at 10:43 Adrian Zubarev via swift-evolution
<[email protected]> wrote:
I still don’t catch to point here. There is no implicit public there. It’s
explicit set by the default access modifier of extensions. It’s how they work
and how they should remain (at least as long the community want default access
modifier to exist on extensions). Disallowing setting public on extensions when
you extend a public type makes no sense. If you want your member to be internal
like it’s in types, then remove the access modifier from extension and all
member will follow the type access modifier.
--
Adrian Zubarev
Sent with Airmail
Am 17. Juli 2016 um 17:37:02, Xiaodi Wu ([email protected]) schrieb:
That's a good point. I will incorporate these into a revised draft. Only two
things will change:
```
public struct Foo {
// implicitly internal
func frobnicate1() { }
}
public extension Foo {
// currently implicitly public
//
// depending on which alternative is adopted,
// the proposal will either prohibit `public extension`
// or this method will be implicitly internal
func frobnicate2() { }
}
```
```
internal struct Bar {
// permitted by SE-0025 without a warning
// this method can only be accessed within module anyway
// because `internal struct` bounds access of its members
public func frobnicate1() { }
}
extension Bar {
// not permitted by SE-0025
//
// after proposal, this will also be permitted without a warning
// and this method will also be accessible only within module
public func frobnicate2() { }
}
```
On Sun, Jul 17, 2016 at 1:50 AM, Adrian Zubarev via swift-evolution
<[email protected]> wrote:
I’m struggling to understand your proposal, can you provide some specific code
samples how it works now and what will change. The example from the draft
doesn’t help my understanding. :/
--
Adrian Zubarev
Sent with Airmail
Am 17. Juli 2016 um 04:40:45, Xiaodi Wu via swift-evolution
([email protected]) schrieb:
On Sat, Jul 16, 2016 at 7:56 PM, Jose Cheyo Jimenez <[email protected]> wrote:
I think you can simplify this proposal by just saying something like this and
give a couple of examples that are easy to follow:
Disallow explicit public access modifier on non-protocol-conforming type
extensions.
It took me a while to process what you're trying to say here, but this is a
good idea and would go along well with the first draft's proposed solution. I
will spell it out. (If we say that you can use an explicit modifier only to
lower the access level of members, then `public` as an explicit modifier could
be entirely disallowed.)
I think if you only focus on that breaking change then the proposal will have a
good chance of getting accepted and fixing the immediate issue of public. There
is a reason why protocol conforming extensions do not allow explicitly saying
public
`public extension Type: Protocol {}` // public not allowed
Actually, no modifiers are allowed in that scenario, IIUC.
In essence we will be asking for the same behavior for types.
Allowing methods declared inside extensions to have a higher declared
visibility is not a breaking change and can be introduced later.
It is a breaking change in that I am proposing that the rules be harmonized so
that the implicit default access level will be notionally `internal` (there are
follow-on benefits to this change). That cannot be changed later.
Nobody wants private extensions or implicit internal extensions to go away. :)
I know that there are people who don't want it to go away. That was why the
first draft proposed keeping them, but it sounds like it would make for an
illogical system. I know that Jordan and John have both indicated that they
don't think it's worth keeping around but don't seem to feel too strongly about
it, and I think I feel the same way (leaning towards not keeping them, but
don't feel very strongly). I will definitely feature this concern (using
extensions as access modifier groups) prominently in the proposal and hope for
a robust discussion to see how it plays out with the community and core team.
On Jul 16, 2016, at 4:22 PM, Xiaodi Wu via swift-evolution
<[email protected]> wrote:
On Sat, Jul 16, 2016 at 6:10 PM, David Hart <[email protected]> wrote:
This proposal really confuses me. Two comments:
1) With the proposal, we loose the ability to use access modifiers on
extensions as a way of grouping members by access. That's a huge loss for me.
You lose the ability to group public members only. That part is intentional, so
that only methods declared with `public func` are public.
2) If we adopt the proposal, I now have no idea what explicit access modifiers
on extensions do.
I propose keeping explicit access modifiers because previous comments on this
list have said that it's useful for grouping members by access. You can
continue to use extensions to group fileprivate members of an internal type, or
internal members of a public type.
More generally, I don't understand this proposal as it's trying to apply the
same access modifier rules on extensions as for types but extensions are not
types. They are just a declaration for extending types which already have an
access level.
On 16 Jul 2016, at 20:04, Xiaodi Wu via swift-evolution
<[email protected]> wrote:
With the impending withdrawal of SE-0119 and the closing window for (most)
source-breaking changes, I thought I'd draft up a proposal to address some of
the key points raised in that discussion.
The proposed changes are deliberately limited in scope to rationalizing access
modifier rules without adding any new facilities (such as conformances of lower
visibility than the type), which might be more appropriate for the Swift 4
timeline.
I hope this will prove satisfactory to the community :)
Harmonize access modifiers for extensions
Proposal: SE-XXXX
Author: Xiaodi Wu
Status: Awaiting review
Review manager: TBD
Introduction
During discussion of SE-0119, the community articulated the view that access
modifiers for extensions were and should continue to be subject to the same
rules as access modifiers for types. Unfortunately, it is not factually true
today; this proposal aims to make it so.
Swift-evolution threads:
[Proposal] Revising access modifiers on extensions
[More to be added here]
Motivation
Consider the following:
public struct foo {
func frobnicate() { } // implicitly internal
}
public extension foo { }
public struct bar { }
public extension bar {
func frobnicate() { } // implicitly public, according to SE-0025
}
According to SE-0025, a method moved from the body of a public struct into a
public extension becomes public without modification. This is surprising
behavior contrary to Swift's general rule of not exposing public API by default.
Furthermore, SE-0025 now permits the owner of a type to design access for
members as though the type will have a higher access level than it currently
does. For example, users will be able to design public methods inside an
internaltype before "flipping the switch" and making that type public. The same
approach is prohibited by SE-0025 for extensions, although conceptually it need
not be.
Proposed solution
The proposed solution is to change access modifier rules for extensions with
the following effect: if any method (or computed property) declared within the
body of a type at file scope is moved without modification into the body of an
extension in the same file, the move will not change its accessibility.
In code:
struct foo {
// Any method declared here...
}
extension foo {
// ...should have the same visibility when moved here.
}
This implies that public API commitments will need to be annotated as public at
declaration sites inside an extension just as it must be at declaration sites
inside types.
Detailed design
Declarations inside the extension will, like declarations inside types, have a
default access level of internal.
The compiler should not warn when a broader level of access control is used for
a method (or computed property, etc.) declared within an extension with more
restrictive access. This allows the owner of the extension to design the access
level they would use for a method if the type or extension were to be made more
widely accessible.
An extension declared without an explicit access modifier will have the same
access level as the type being extended.
An extension declared without protocol conformance may optionally use an
explicit access modifier to provide an upper bound for the visibility of its
members.
Alternatives considered
One alternative, still open for consideration, is to eliminate #4 and disallow
explicit access modifiers on extensions. As an advantage, this would clarify
the mental model that extensions are not their own entities, as they cannot be
referred to by name and have no runtime representation. As a disadvantage,
extensions cease to be an access modifier grouping construct, which some users
really like.
Acknowledgments
Thanks to all discussants on the list, especially Adrian Zubarev and Jose Cheyo
Jimenez.
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
