[swift-users] How self automatically becomes Self type if the function's return type is Self?

[Zhao Xin]

Thanks, Kenny. I found that self is dynamic. Despite the original type of
 variable. See below code, `test` variable. It was Foo type, but it can be
Bar as well.

class Foo { func printType() { print(type(of:self)) } func printSelf() {
print(self) } } class Bar:Foo { } let foo = Foo() foo.printType() // Foo
foo.printSelf() // Foo let bar = Bar() bar.printType() // Bar
bar.printSelf() // Bar var test = Foo() test.printType() // Foo
test.printSelf() // Foo test = Bar() test.printType() // Bar
test.printSelf() // Bar


​So now I think that self should always be Self type.​


Zhaoxin

On Sun, Aug 28, 2016 at 2:05 PM, Kenny Leung via swift-users <
swift-users at swift.org> wrote:

> There is no magic happening here. Rather, I think it’s a misunderstanding
> of what -> Self means. Self is a placeholder for “the current type”, just
> like self is a placeholder for “the current instance”. So when you declare
> -> Self, the correct thing to do is an instance of Self, which is self.
>
> You can see this if you replace Self with String.
>
> protocol Foo {
>     func instance() -> String
> }
>
> class Bar: Foo {
>     func instance() -> String {
>        return “blah"
>     }
> }
>
> -Kenny
>
>
> > On Aug 27, 2016, at 7:05 AM, Zhao Xin via swift-users <
> swift-users at swift.org> wrote:
> >
> > See the code:
> >
> > protocol Foo {
> >     func instance() -> Self
> > }
> >
> > class Bar: Foo {
> >     func instance() -> Self {
> >         return self // Declaration: let `self`: Self
> >     }
> >     func other() {
> >         let i = self // Declaration: let `self`: Bar
> >     }
> > }
> >
> > How does it happen?
> >
> > Zhaoxin
> > _______________________________________________
> > swift-users mailing list
> > swift-users at swift.org
> > https://lists.swift.org/mailman/listinfo/swift-users
>
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