[swift-evolution] Ability to set access control independently for getter & setter of a property

[Johan Jensen]

For reference, it can also be found in The Swift Programming Language Guide
under Access Control › Constants, Variables, Properties, and
Subscripts › Getters
and Setters
<https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/AccessControl.html#//apple_ref/doc/uid/TP40014097-CH41-ID18>
.

> You can give a setter a *lower* access level than its corresponding
getter, to restrict the read-write scope of that variable, property, or
subscript. You assign a lower access level by writing private(set) or
internal(set) before the var or subscript introducer.

—Johan

On Fri, Dec 4, 2015 at 8:57 PM, Evan Maloney <emaloney at gilt.com> wrote:

> Very cool! I hadn't seen that in use anywhere; glad I sent my e-mail or I
> wouldn't know it exists. :)
>
> Thanks, Jordan!
>
>
>
> On Dec 4, 2015, at 2:50 PM, Jordan Rose <jordan_rose at apple.com> wrote:
>
> We have this, actually! It's spelled "private(set)" on the property.
>
> We probably will need a way to put attributes on stored property
> accessors, though. @objc for custom getter or setter names is an
> interesting one already.
>
> Jordan
>
>
> On Dec 4, 2015, at 11:48 , Evan Maloney <emaloney at gilt.com> wrote:
>
> Currently, Swift supports a single level of access controls for
> properties. If a read/write property is declared as public, both the getter
> and the setter of that property will be publicly visible.
>
> However, it is often the case that you need a stored property that is
> publicly read-only but internally or privately writeable. The current way
> to achieve this is by doing something like:
>
>     public var authenticationValidUntil: NSDate? {
>         return _authenticationValidUntil
>     }
>     private var _authenticationValidUntil: NSDate?
>
> This seems like a lot of boilerplate to achieve a common goal. Objective-C
> supported a similar concept by being able to declare a property as
> read-only in a .h file while being able to override this as a read-write
> property in the .m file.
>
> I propose being able to declare separate access controls for a property's
> getter and setter, wherein the setter could have more restrictive access
> controls than the getter.
>
> For example:
>
>     var authenticationValidUntil: NSDate? { public get, private set }
>
> This would result in a public getter, while the implementer could still
> set the value of the property.
>
> Curious to get your thoughts on this.
>
> Regards,
>
> E. Maloney
> Gilt Groupe
>
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