SE-0025: Scoped Access Level, next steps

Patrick_Pijnappel · March 16, 2016, 6:49am

Ok to summarize:

*Setter access modifiers*

var foo: Int { private set { ... } }

var foo: Int { private set }

   - Consistent with mutating set { ... }. Arguably the current private(set)
   is inconsistent.
   - Eliminates the odd corner case of having a double access modifier,
   e.g. public private(set) var foo: Int.
   - It's very sensible for custom getters/setters (top case), it just
   requires allowing a bodiless get/set. We already kinda do this in protocols.

*Access modifier keywords*

public/private(module)/private(file)/private

   - It's not clear from the keywords how restrictive local/private/internal
   are, while private(module) and private(file) are obvious. This
makes a declaration
   either public, or private to a certain scope. Arguably e.g.
   public/module/file/declaration has similar benefits but they aren't as
   clearly access control related as a keyword (e.g. module could just as
   well be declaring a module).
   - private(module) and private(file) are relatively long, but the longest
   – private(module) – is rarely used (outside the standard library) as
   it's the default. Most uses of the old private are more appropriately
   done using the new private, so private(file) would likely be used less
   than private.
   - The scheme expands very well to named submodules, e.g. if you have a
   submodule named model you might limit the scope using private(model).
   - private(file) as opposed to private-file or private/file makes it more
   consistent with the new function-like syntax for e.g. attributes.

···

On Wed, Mar 16, 2016 at 11:26 AM, Ross O'Brien via swift-evolution < swift-evolution@swift.org> wrote:

It's occurring to me, reading these recent posts, that we have two
orthogonal systems of access levels.

Swift's current access system is file based; a project file decides which
files comprise a module, and the terms 'public', 'internal' and 'private'
determine whether a property is accessible to all, accessible only within
files of the module, or accessible only within a file. (This takes on an
extra dimension as files may belong to several modules).

The concept which began this discussion, and several of the proposed
concepts in this discussion, ask instead for a type-based access system
similar to those in other languages including Objective-C, where 'public',
'protected' and 'private' are the terms of choice and they restrict access
to a type or subtypes.

I think it would be confusing if Swift applied 'public' to a concept in
the file-based access system and 'private' to a concept in the type-based
access system.

I would prefer clearer terms which actually mention the restrictions of
the level. For example, 'inherited', not 'protected', in the case of
properties accessible by a class and its subclasses; 'declaration', rather
than 'private' or 'scoped', to refer to properties only accessible within a
given type or extension declaration.

Since, at the moment, a declaration can only occur within one file, I
think this most-restricted level has managed to pass as a level of the
file-based access system. However, if the system is ever extended, we're
going to run into new syntax decisions where we have 'private module'
functions (accessible only within the given type in the same module) trying
to communicate with 'protected file' properties (accessible only with the
type and its subtypes in the same file), and that might lead to conflicts,
so perhaps we should decide how those might be declared now.

On Tue, Mar 15, 2016 at 11:51 PM, Jonathan Hull via swift-evolution < > swift-evolution@swift.org> wrote:

On Tue, Mar 15, 2016 at 2:33 PM Erica Sadun <erica at ericasadun.com <https://lists.swift.org/mailman/listinfo/swift-evolution>> wrote:

And again, moving the access control modification to the end just doesn't look
right to me or seem to enhance readability. :(

I like Shawn’s proposal better for cases where there are custom
getter/setter implementations. We should definitely be able to do:

var foo:Int {
public get {…}
private(file) set {…}
}

In fact, that is what I first tried to do before learning about
private(set). But without the implementations, it just seems strange to
put the scoping after the rest of the declaration (they work above because
they are *before* the custom getter/setter).

I still like the idea of having the option to use parameter-like syntax
for cases where you don’t have custom getters/setters:

private var foo:Int
private(file) var foo:Int
private(set: file) var foo:Int
private(get: global, set: file) var foo:Int

I guess, if we had some way to represent the standard getter/setter, that
might work too. I don’t love it, but maybe with better wording?

var foo:Int{
public get useDefault
private(file) set {…}
}

Thanks,
Jon

On Mar 14, 2016, at 10:22 PM, Patrick Pijnappel < >> patrickpijnappel@gmail.com> wrote:

I like Shawn's proposal:

var foo: Int { private(file) set }

In fact it's probably more sensible than the current private(set) IMO.

For example, we already use

var foo: Int { mutating get { ... } }

and not

mutating(get) var foo: Int { get { ... } }

On Tue, Mar 15, 2016 at 4:13 PM, Patrick Pijnappel < >> patrickpijnappel@gmail.com> wrote:

I like Shawn's proposal:

var foo: Int { private(file) set }

In fact it's probably more sensible than the current private(set) IMO.

While I like private(get: file, set: module) idea, I think it just gets
too inconsistent with private(set: public) and private(set: private)
(?!)

On Tue, Mar 15, 2016 at 3:39 PM, Jonathan Hull via swift-evolution < >>> swift-evolution@swift.org> wrote:

*On Mar 14, 2016, at 8:36 PM, Patrick Pijnappel via swift-evolution <swift-evolution at swift.org <https://lists.swift.org/mailman/listinfo/swift-evolution>> wrote:*

The only question is (as Sean mentioned) how this combines with the syntax
for setter access level, e.g. the current private(set). Options:
- Unnamed 2nd argument, giving private(file), private(file, set),
private(set).
- Named 2nd argument, giving e.g. private(file), private(file, accessor:
set), private(accessor: set). Less ambiguity but longer.
- Not using multiple arguments, but that'd probably break consistency with
the other unification efforts going on to make everything look like
function calls.

What about the following 3 forms?

private(file) //both setter and getter have file scope
private(set: file) //setter has file scope. Equivalent to current
“private(set)"
private(get: module, set: file) //getter has module scope & setter has
file scope

It is a bit weird, but we should probably also allow “public" in that
last form: private(get: public, set: module)

Thanks,
Jon

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