[swift-users] Why can't Swift instance methods call class methods without qualification?

Kate Stone k8stone at apple.com
Fri Jul 1 13:06:24 CDT 2016

> On Jul 1, 2016, at 11:01 AM, Jens Alfke via swift-users <swift-users at swift.org> wrote:
>> On Jul 1, 2016, at 10:28 AM, Nicholas Outram via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>> class methods may mutate "mutable static variables” (singletons), which are dangerous in multi-threaded code.
> This is the same argument zh ao made. But instance methods may also mutate static variables, so the fact that you’re calling a class method doesn’t make the call any more dangerous.
> Moreover, mutating instance variables can be just as dangerous for multithreaded code (and is a more frequent source of bugs IMHO).
> Really, the only significant difference is that a class method can’t modify instance variables, so from that perspective it’s actually a bit safer than an instance method call!

Though that isn’t strictly true for singleton patterns and other reasons why class variables might include references to instances.

I believe there’s real value in being explicit about referencing class members.  It helps both the reader of the code and it makes writing code with typical IDE conveniences like code completion less cluttered and more informative. Unfamiliar class methods won’t be included in lists of suggestions where they might look like they operate on the current instance.

Kate Stone k8stone at apple.com <mailto:k8stone at apple.com>
 Xcode Low Level Tools

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