[swift-users] @objc and private methods

[Zhao Xin]

I think @objc makes the function an Objective-C function, so the private is
no longer making the function private in Swift way, but in Objective-C way.
In C++,  sub-class can call super-class's private method. What you have to
do is to override the function.

class Test {

    @objc private func somefunc() {

        print( "hello 1" )

    }

}


class Test2: Test {

    @objc override private func somefunc() {

        print( "hello 2" )

    }

}



Zhaoxin




On Thu, Jul 21, 2016 at 10:25 PM, Tod Cunningham via swift-users <
swift-users at swift.org> wrote:

> I wanted to get thoughts on the use of @objc and private methods.  Should
> this usage be avoided or leveraged?
>
> I have seen some code where things like UIButton and Gesture recognizer
> handlers are defined as being private.  I would have thought this would
> result in a compiler error given objective-c doesn’t support private
> accessors.  However, it compiles and works as expected (kind of).
>
> One plus for defining the handlers as private is they aren’t visible to
> swift outside of the file they are defined in.  The problem is you can run
> into some issues with inheritance if you define the same handler in a
> derived class.  Take the following simple example:
>
> class Test {
>     @objc private func somefunc() {
>         print( "hello 1" )
>     }
> }
>
> -- in another file –
>
> class Test2: Test {
>     @objc private func somefunc() {
>         print( "hello 2" )
>     }
> }
>
> This will result in the following compiler error:
>
> Method 'somefunc()' with Objective-C selector 'somefunc' conflicts with
> method 'somefunc()' from superclass 'Test' with the same Objective-C
> selector
>
> That error makes sense in an Objective-C context as Test2 has two
> different methods defined with the same objective-c selector (somefunc).
> Swift can tell them apart as they are private to each class, but Obj-C
> can’t tell them apart as they have the same selector thus the error.
>
> One workaround would be to give the method a different Objective-C names
> such as @objc(test2_somefunc); however, that could really lead to some
> unexpected results depending on what selector is used to call somefunc.
> Test2 would need to “register” a different selector for somefunc then Test
> does for whatever is calling it on the Objective-C side (yuck!).
>
> This can of course be solved by not making the method private which allows
> Test2 to explicitly override somefunc.
>
> class Test {
>    @objc func somefunc() {
>        print( "hello 1" )
>    }
> }
>
> -- in another file –
>
> class Test2: Test {
>    @objc override func somefunc() {
>        print( "hello 2" )
>    }
> }
>
> I would say that when declaring @objc methods they shouldn’t be private
> and should have the same (public/internal) access method as their
> containing class.  What’s your thoughts?  Why does swift allow a method to
> be declared as both @objc and private?
>
> Thanks,
>
>
>
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