[swift-evolution] [Proposal] Warn about implicit property access in own setter

Marc Knaup marc at knaup.koeln
Wed Dec 16 07:24:01 CST 2015

Whether or not an explicit parameter name for property setters (and
observers) is enforced (instead of implicit newValue and oldValue) should
be a distinct proposal with its on discussion.
Even with explicit parameter names you can still accidentally refer to the
getter where you actually mean the new value if you don't give the
parameter exactly the same name.

When migrating existing code by adding an explicit newValue parameter name
then that code will still have this bug since the implicit access to the
getter is still neither fixed nor lamented.

I'll update the proposal accordingly.

On Wed, Dec 16, 2015 at 5:03 AM, Dennis Lysenko <dennis.s.lysenko at gmail.com>

> Caught red handed not having gone through the alternatives! I'm not sure
> the listed negatives are too bad though. Impact on existing source, in
> particular, why is that an issue? Code migration has solved every breaking
> change so far. As for oldValue, yes, I think that should be changed as
> well. Not sure why that is a con. Agreed it makes it more verbose but also
> gives more clarity and the verbosity is negligible and I would say better
> than hidden compiler magic.
> The need for the proposed solution feels a bit like a monkey-patch on top
> of a system that shouldn't need that monkey patch in the first place. That
> said, the proposal, were it accepted as-is, would be a welcome change and
> thanks for writing it up.
> On Tue, Dec 15, 2015, 9:41 PM Marc Knaup <marc at knaup.koeln> wrote:
>> That approach is mentioned in "Alternatives considered".
>> On Dec 16, 2015 03:39, "Dennis Lysenko" <dennis.s.lysenko at gmail.com>
>> wrote:
>>> Other possible solution: why not just remove the default "newValue" and
>>> force the user to manually specify it instead?
>>> On Tue, Dec 15, 2015, 6:02 PM Marc Knaup via swift-evolution <
>>> swift-evolution at swift.org> wrote:
>>>> Hello everyone,
>>>> I would like to propose yielding a warning when a property's getter is
>>>> used from within its setter implicitly without using "self.".
>>>> This can lead to programming errors which are very easy to miss and
>>>> lead to unexpected behavior at runtime.
>>>> Check out the full proposal here:
>>>> https://github.com/fluidsonic/swift-evolution/blob/master/proposals/NNNN-warn-about-implicit-property-access-in-own-setter.md
>>>> Thank you,
>>>>   Marc
>>>> _______________________________________________
>>>> swift-evolution mailing list
>>>> swift-evolution at swift.org
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
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