[swift-users] Initializers

[Slava Pestov]

> On Jan 27, 2017, at 10:39 AM, tuuranton--- via swift-users <swift-users at swift.org> wrote:
> 
> Yes, but why?
> 
> What's the rationale for this?
> 
> What would be so bad about allowing overriding a non-failable initializer with a failable initializer?

If the non-failable initializer witnesses a non-failable protocol requirement, and the subclass overrides it, what should be the runtime behavior if the subclass initializer returns nil? The caller won’t expect it, since the caller is calling a non-failable initializer.

For similar reasons, you cannot override a method that returns a non-optional value with a method returning an optional value.

Slava

> 
> 27. Jan 2017 18:59 by saagar at saagarjha.com <mailto:saagar at saagarjha.com>:
> 
> You can’t override a designated initializer with one that is failable. The second one is defining a new initializer that is failable, instead of overriding the one from its superclass.
> 
> Saagar Jha
> 
> On Jan 27, 2017, at 8:45 AM, tuuranton--- via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
> 
> See the comments. Why is one allowed but the other one isn't and what's the rationale for this?
> 
> 
> class Vehicle {
>     let name: String
>     init(name: String) {
>         self.name = name
>     }
> }
> 
> 
> class Car: Vehicle {
>     //Why is this not allowed?
>     override init?(name: String) {
>         super.init(name: name)
>     }
>     
>     //But this is allowed?
>     init?(name: String, ignore: String) {
>         super.init(name: name)
>     }
> }
> 
> 
> 
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