Re: [swift-users] Weak references in generic types

[Jens Alfke via swift-users]

> On Sep 8, 2016, at 6:28 AM, Karl Wagner via swift-users 
>  wrote:
> 
> It is in some sense a language limitation that we cant express what you're 
> talking about. If we weren't using mailing lists it would be easier to search 
> for "protocol self-conformance" on swift-evo and to read the earlier 
> discussion about it. 



…or if we were using some modern mailing list host like Google Groups or 
groups.io, that also offers a web view.


—Jens___
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Re: [swift-users] Weak references in generic types

[Karl Wagner via swift-users]

  
  
What I'm trying to say is that P is a protocol and not a class, so it does not 
conform to AnyObject.   P does not conform to P.
  

  
It is in some sense a language limitation that we cant express what you're 
talking about. If we weren't using mailing lists it would be easier to search 
for "protocol self-conformance" on swift-evo and to read the earlier discussion 
about it.   
  

  

  
  
>   
> On Sep 2, 2016 at 1:04 am,  mailto:howard.lov...@gmail.com)>  
> wrote:
>   
>   
> @Karl,  
>
>   
> You say "In the second example, you’re creating WeakReference. P does not 
> conform to P or to AnyObject.", but P does conform to AnyObject.
>   
>
>   
> I suspect it is a compiler limitation/ bug.   
>   
>
>   
>   -- Howard.   
>
>  On Thursday, 1 September 2016, Karl   (mailto:razie...@gmail.com)>  wrote:
>   
> >   
> >
> >   
> >   
> > >   
> > > On 1 Sep 2016, at 03:23, Howard Lovatt via swift-users  
> > >  > > (javascript:_e(%7B%7D,'cvml','swift-users@swift.org');)>  wrote:
> > >   
> > >   
> > >   
> > > Playing around I found that if you make the protocol @objc instead of 
> > > AnyObject then it works :). EG:  
> > >
> > >   
> > > >   
> > > > struct WeakReference  {
> > > >   
> > > >weak var value: T?
> > > >   
> > > > }
> > > >   
> > > > @objc protocol P { // Note @objc, class or AnyObject does not work
> > > >   
> > > >var i: Int { get }
> > > >   
> > > > }
> > > >   
> > > > class CP: P {
> > > >   
> > > >var i: Int = 0
> > > >   
> > > > }
> > > >   
> > > > let weakPs: [WeakReference] = [WeakReference(value: cP)] // Note 
> > > > typed as `[WeakReference]`
> > > >   
> > > > print("P: \(weakPs[0].value!.i)") // 0
> > > >   
> > >   
> > >   
> > >
> > > Not a 'pure' Swift solution :(, but OK in my case.
> > >
> > >   
> > >   
> > >   
> > >
> > >   
> > >   
> > >-- Howard.
> > > 
> > >   
> > > On 29 August 2016 at 16:21, Howard Lovatt   > > (javascript:_e(%7B%7D,'cvml','howard.lov...@gmail.com');)>  wrote:
> > >   
> > > >   
> > > > Hi,  
> > > >
> > > >   
> > > > I am wanting to use weak references in generic data structures; in the 
> > > > example below Array, but in general any generic type. I can almost get 
> > > > it to work :(
> > > >   
> > > >
> > > >   
> > > > My experiments started off well; the following works:
> > > >   
> > > >
> > > >   
> > > > >   
> > > > > // Array of weak references OK
> > > > >   
> > > > > struct WeakReference  {
> > > > >   
> > > > >weak var value: T?
> > > > >   
> > > > > }
> > > > >   
> > > > > class C {
> > > > >   
> > > > >var i: Int = 0
> > > > >   
> > > > > }
> > > > >   
> > > > > let c = C() // Strong reference to prevent collection
> > > > >   
> > > > > let weakCs = [WeakReference(value: c)] // OK
> > > > >   
> > > > > print("C: \(weakCs[0].value!.i)") // 0
> > > > >   
> > > >   
> > > >  I can add a protocol:  
> > > >
> > > >   
> > > > >   
> > > > > // Array of weak references that implements a protocol OK
> > > > >   
> > > > > protocol P: AnyObject { // Note AnyObject
> > > > >   
> > > > >var i: Int { get }
> > > > >   
> > > > > }
> > > > >   
> > > > > class CP: P {
> > > > >   
> > > > >var i: Int = 0
> > > > >   
> > > > > }
> > > > >   
> > > > > let cP = CP() // Strong reference to prevent collection
> > > > >   
> > > > > let weakCPs = [WeakReference(value: cP)] // OK
> > > > >   
> > > > > print("CP: \(weakCPs[0].value!.i)") // 0
> > > > >   
> > > >   
> > > >   
> > > >
> > > >   
> > > > But when I want an array of weak references to the protocol I get an 
> > > > error:
> > > >   
> > > >
> > > > 
> > > > >   
> > > > > // Array of weak references of a protocol not OK
> > > > >   
> > > > > let weakPs: [WeakReference] = [WeakReference(value: cP)] // Using 
> > > > > 'P' as a concrete type conforming to protocol 'AnyObject' is not 
> > > > > supported
> > > > >   
> > > > > print("P: \(weakPs[0].value!.i)") // 0
> > > > >   
> > > >   
> > > >   
> > > >
> > > >   
> > > > Is there something I have missed?
> > > >   
> > > >
> > > >   
> > > > The error message, "Using 'P' as a concrete type conforming to protocol 
> > > > 'AnyObject' is not supported", implies that it is a temporary 
> > > > limitation of the compiler; is this going to be fixed? Should I lodge a 
> > > > bug report?
> > > >   
> > > >
> > > >   
> > > > Thanks in advance for any advice,
> > > >   
> > > >
> > > >   
> > > >   
> > > >-- Howard.
> > > >   
> > >  ___
> > >  swift-users mailing list
> > >   swift-users@swift.org 
> > > (javascript:_e(%7B%7D,'cvml','swift-users@swift.org');)
> > >   https://lists.swift.org/mailman/listinfo/swift-users
> > > 
> >   
> > Your problem is protocol self-conformance. In the first example, you’re 
> > creating WeakReference. CP conforms to P and to AnyObject. In the 
> > 

Re: [swift-users] Weak references in generic types

[Howard Lovatt via swift-users]

@Karl,

You say "In the second example, you’re creating WeakReference. P does
not conform to P or to AnyObject.", but P does conform to AnyObject.

I suspect it is a compiler limitation/ bug.

 -- Howard.

On Thursday, 1 September 2016, Karl  wrote:

>
> On 1 Sep 2016, at 03:23, Howard Lovatt via swift-users <
> swift-users@swift.org
> > wrote:
>
> Playing around I found that if you make the protocol @objc instead of
> AnyObject then it works :). EG:
>
> struct WeakReference {
> weak var value: T?
> }
> @objc protocol P { // Note @objc, class or AnyObject does not work
> var i: Int { get }
> }
> class CP: P {
> var i: Int = 0
> }
> let weakPs: [WeakReference] = [WeakReference(value: cP)] // Note typed
> as `[WeakReference]`
> print("P: \(weakPs[0].value!.i)") // 0
>
> Not a 'pure' Swift solution :(, but OK in my case.
>
>   -- Howard.
>
> On 29 August 2016 at 16:21, Howard Lovatt  > wrote:
>
>> Hi,
>>
>> I am wanting to use weak references in generic data structures; in the
>> example below Array, but in general any generic type. I can almost get it
>> to work :(
>>
>> My experiments started off well; the following works:
>>
>> // Array of weak references OK
>> struct WeakReference {
>> weak var value: T?
>> }
>> class C {
>> var i: Int = 0
>> }
>> let c = C() // Strong reference to prevent collection
>> let weakCs = [WeakReference(value: c)] // OK
>> print("C: \(weakCs[0].value!.i)") // 0
>>
>>
>> I can add a protocol:
>>
>> // Array of weak references that implements a protocol OK
>> protocol P: AnyObject { // Note AnyObject
>> var i: Int { get }
>> }
>> class CP: P {
>> var i: Int = 0
>> }
>> let cP = CP() // Strong reference to prevent collection
>> let weakCPs = [WeakReference(value: cP)] // OK
>> print("CP: \(weakCPs[0].value!.i)") // 0
>>
>>
>> But when I want an array of weak references to the protocol I get an
>> error:
>>
>> // Array of weak references of a protocol not OK
>> let weakPs: [WeakReference] = [WeakReference(value: cP)] // Using 'P'
>> as a concrete type conforming to protocol 'AnyObject' is not supported
>> print("P: \(weakPs[0].value!.i)") // 0
>>
>>
>> Is there something I have missed?
>>
>> The error message, "Using 'P' as a concrete type conforming to protocol
>> 'AnyObject' is not supported", implies that it is a temporary limitation of
>> the compiler; is this going to be fixed? Should I lodge a bug report?
>>
>> Thanks in advance for any advice,
>>
>>   -- Howard.
>>
>
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> 
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>
>
> Your problem is protocol self-conformance. In the first example, you’re
> creating WeakReference. CP conforms to P and to AnyObject. In the
> second example, you’re creating WeakReference. P does not conform to P
> or to AnyObject.
>
> As for why @objc fixes it? … ¯\_(ツ)_/¯ all bets are off whenever @objc
> gets involved in anything.
>
> Karl
>


-- 
-- Howard.
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Re: [swift-users] Weak references in generic types

[Howard Lovatt via swift-users]

Playing around I found that if you make the protocol @objc instead of
AnyObject then it works :). EG:

struct WeakReference {
weak var value: T?
}
@objc protocol P { // Note @objc, class or AnyObject does not work
var i: Int { get }
}
class CP: P {
var i: Int = 0
}
let weakPs: [WeakReference] = [WeakReference(value: cP)] // Note typed
as `[WeakReference]`
print("P: \(weakPs[0].value!.i)") // 0

Not a 'pure' Swift solution :(, but OK in my case.

  -- Howard.

On 29 August 2016 at 16:21, Howard Lovatt  wrote:

> Hi,
>
> I am wanting to use weak references in generic data structures; in the
> example below Array, but in general any generic type. I can almost get it
> to work :(
>
> My experiments started off well; the following works:
>
> // Array of weak references OK
> struct WeakReference {
> weak var value: T?
> }
> class C {
> var i: Int = 0
> }
> let c = C() // Strong reference to prevent collection
> let weakCs = [WeakReference(value: c)] // OK
> print("C: \(weakCs[0].value!.i)") // 0
>
>
> I can add a protocol:
>
> // Array of weak references that implements a protocol OK
> protocol P: AnyObject { // Note AnyObject
> var i: Int { get }
> }
> class CP: P {
> var i: Int = 0
> }
> let cP = CP() // Strong reference to prevent collection
> let weakCPs = [WeakReference(value: cP)] // OK
> print("CP: \(weakCPs[0].value!.i)") // 0
>
>
> But when I want an array of weak references to the protocol I get an error:
>
> // Array of weak references of a protocol not OK
> let weakPs: [WeakReference] = [WeakReference(value: cP)] // Using 'P'
> as a concrete type conforming to protocol 'AnyObject' is not supported
> print("P: \(weakPs[0].value!.i)") // 0
>
>
> Is there something I have missed?
>
> The error message, "Using 'P' as a concrete type conforming to protocol
> 'AnyObject' is not supported", implies that it is a temporary limitation of
> the compiler; is this going to be fixed? Should I lodge a bug report?
>
> Thanks in advance for any advice,
>
>   -- Howard.
>
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[swift-users] Weak references in generic types

[Howard Lovatt via swift-users]

Hi,

I am wanting to use weak references in generic data structures; in the
example below Array, but in general any generic type. I can almost get it
to work :(

My experiments started off well; the following works:

// Array of weak references OK
struct WeakReference {
weak var value: T?
}
class C {
var i: Int = 0
}
let c = C() // Strong reference to prevent collection
let weakCs = [WeakReference(value: c)] // OK
print("C: \(weakCs[0].value!.i)") // 0


I can add a protocol:

// Array of weak references that implements a protocol OK
protocol P: AnyObject { // Note AnyObject
var i: Int { get }
}
class CP: P {
var i: Int = 0
}
let cP = CP() // Strong reference to prevent collection
let weakCPs = [WeakReference(value: cP)] // OK
print("CP: \(weakCPs[0].value!.i)") // 0


But when I want an array of weak references to the protocol I get an error:

// Array of weak references of a protocol not OK
let weakPs: [WeakReference] = [WeakReference(value: cP)] // Using 'P' as
a concrete type conforming to protocol 'AnyObject' is not supported
print("P: \(weakPs[0].value!.i)") // 0


Is there something I have missed?

The error message, "Using 'P' as a concrete type conforming to protocol
'AnyObject' is not supported", implies that it is a temporary limitation of
the compiler; is this going to be fixed? Should I lodge a bug report?

Thanks in advance for any advice,

  -- Howard.
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