[swift-users] super.init() called automatically?

Chris Lattner clattner at apple.com
Mon May 16 12:29:59 CDT 2016


> On May 16, 2016, at 7:09 AM, tuuranton--- via swift-users <swift-users at swift.org> wrote:
> 
> Why does the following code compile?
> Why does Bar's init(x: Int) automatically call Foo's init()?
> Why don't I have to manually call super.init() myself?

This is intentional behavior.  It kicks in when your super class has a single designated initializer with a zero-argument init.  This is why you don’t have to call super.init() when deriving from NSObject.

-Chris

> 
> What passage of
> https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Initialization.html#//apple_ref/doc/uid/TP40014097-CH18-ID203 <https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Initialization.html#//apple_ref/doc/uid/TP40014097-CH18-ID203>
> tells me that this should be the case?
> 
> --------------------
> class Foo {
>     init() {
>         print("foo init")
>     }
> }
> class Bar: Foo {
>     init(x: Int) {
>         print("bar init")
>     }
> }
> let b = Bar(x: 0)
> //prints:
> //    bar init
> //    foo init
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