> On Mar 29, 2017, at 10:51 AM, Jens Alfke <[email protected]> wrote:
>
>> On Mar 29, 2017, at 6:57 AM, Daryle Walker <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> Sometimes, I see something in Apple’s AppKit/Foundation reference site that
>> mentions that their technique should be loaded early in the program by
>> putting it in the class’s “+initiallize” method.
>
> A +initialize method doesn’t necessarily run early in the program; it runs
> before the first time a method of that class is called. But that class might
> not be called until later in the process, or never. So +initialize is useful
> for setting up state that this specific class will depend on — like
> initializing static variables — but not for program-wide dependencies.
>
> There’s a more obscure method +load that _does_ get called when the process
> starts up (at roughly the same time as C++ static initializer methods.) Its
> use is discouraged because doing stuff at launch time is bad for
> responsiveness, and because it’s easy to run into problems with dependencies
> on other stuff being initialized already, like if your +load method calls
> something in AppKit that hasn’t been initialized yet because _its_ +load
> method runs after yours…
+load isn’t exposed to Swift either, so that’s not going to work either. You’re
going to have to roll your own replacement for +initialize. Here’s how I’ve
been doing it:
class Foo {
private static let _classInitializer: Void = {
// do your initialization here
}()
init() {
// all static variables are lazy, so be sure not to forget to put this
at the top of *all* your designated initializers or it won’t happen
_ = Foo._classInitializer
}
}
This will ensure that your initialization code will run the first time an
object of the class is created, which is similar to what +initialize does (but
not exact, I know).
>> Now the new Xcode release notes say that “• Swift now warns when an NSObject
>> subclass attempts to override the initialize class method, because Swift
>> can't guarantee that the Objective-C method will be called. (28954946)”
>
> Huh, I haven’t heard of that. And I’m confused by “the Objective-C method” —
> what’s that? Not the +initialize method being compiled, because that’s in
> Swift. The superclass method?
>
> Guess I’ll follow that Radar link and read the bug report myself. Oh, wait. :(
You actually can this time, since Swift’s bug reporter is actually open to the
public. https://bugs.swift.org/browse/SR-3114
<https://bugs.swift.org/browse/SR-3114>
Basically, with Whole Module Optimization turned on, +initialize wasn’t getting
called. Their solution was to just get rid of +initialize.
Charles
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