Re: [swift-evolution] [discussion] Class stored properties?

[Christopher Kornher via swift-evolution]

Class variables are not common, but they are the most natural way to implement 
class-specific functionality. Off the top of my head, I have used class 
variables for:

1) Custom allocation schemes, e.g. pools, LRU implementations
2) Diagnostics, e.g. counting the number of instances of a given class
3) Plugin-in functionality, e.g. customizing behavior of a class at runtime. In 
Swift, the variables would be closures.


You can argue that class variables these are not strictly necessary for these 
tasks, but I have found them to be handy, including during development and 
“Bring-up"

- Chris




> On Aug 9, 2017, at 12:52 PM, Mathew Huusko V via swift-evolution 
>  wrote:
> 
> I don't follow. What's a singleton/how? If you mean my example, the whole 
> point/need for the feature is so it's not. I want `.value` to be unique 
> storage for each subclass.
> 
> On Wed, Aug 9, 2017 at 7:09 PM, Robert Widmann  > wrote:
> This is a singleton, it just happens to be in class scope.
> 
> ~Robert Widmann
> 
> > On Aug 9, 2017, at 3:55 AM, Mathew Huusko V via swift-evolution 
> > mailto:swift-evolution@swift.org>> wrote:
> >
> > Curious if class stored properties have ever been discussed (doesn't seem 
> > so..)?
> >
> > Also, assuming no, and assuming there's a good reason no/they're not coming 
> > anytime soon, what are some patterns people have been using in their place? 
> > I was considering something like..
> >
> > class SomeClass {
> > private static var _classValues = [SomeClass.Type: Int]()
> >
> > class var value: Int {
> > get { _classValues[self] }
> > set { _classValues[self] = newValue }
> > }
> > }
> >
> > .. but then I remembered types aren't hashable yet either (so I guess I 
> > need to stringify it first).
> > ___
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> > swift-evolution@swift.org 
> > https://lists.swift.org/mailman/listinfo/swift-evolution 
> > 
> 
> 
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Re: [swift-evolution] [discussion] Class stored properties?

[Mathew Huusko V via swift-evolution]

I don't follow. What's a singleton/how? If you mean my example, the whole
point/need for the feature is so it's not. I want `.value` to be unique
storage for each subclass.

On Wed, Aug 9, 2017 at 7:09 PM, Robert Widmann  wrote:

> This is a singleton, it just happens to be in class scope.
>
> ~Robert Widmann
>
> > On Aug 9, 2017, at 3:55 AM, Mathew Huusko V via swift-evolution <
> swift-evolution@swift.org> wrote:
> >
> > Curious if class stored properties have ever been discussed (doesn't
> seem so..)?
> >
> > Also, assuming no, and assuming there's a good reason no/they're not
> coming anytime soon, what are some patterns people have been using in their
> place? I was considering something like..
> >
> > class SomeClass {
> > private static var _classValues = [SomeClass.Type: Int]()
> >
> > class var value: Int {
> > get { _classValues[self] }
> > set { _classValues[self] = newValue }
> > }
> > }
> >
> > .. but then I remembered types aren't hashable yet either (so I guess I
> need to stringify it first).
> > ___
> > swift-evolution mailing list
> > swift-evolution@swift.org
> > https://lists.swift.org/mailman/listinfo/swift-evolution
>
>
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Re: [swift-evolution] [discussion] Class stored properties?

[Robert Widmann via swift-evolution]

This is a singleton, it just happens to be in class scope.

~Robert Widmann

> On Aug 9, 2017, at 3:55 AM, Mathew Huusko V via swift-evolution 
>  wrote:
> 
> Curious if class stored properties have ever been discussed (doesn't seem 
> so..)?
> 
> Also, assuming no, and assuming there's a good reason no/they're not coming 
> anytime soon, what are some patterns people have been using in their place? I 
> was considering something like..
> 
> class SomeClass {
> private static var _classValues = [SomeClass.Type: Int]()
> 
> class var value: Int {
> get { _classValues[self] }
> set { _classValues[self] = newValue }
> }
> }
> 
> .. but then I remembered types aren't hashable yet either (so I guess I need 
> to stringify it first).
> ___
> swift-evolution mailing list
> swift-evolution@swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

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Re: [swift-evolution] [discussion] Class stored properties?

[Charlie Monroe via swift-evolution]

It's common for a class to return a value (class var), but setting it on a 
per-class basis IMHO isn't *that* common. But maybe I'm mistaken.

> On Aug 9, 2017, at 1:09 PM, Mathew Huusko V  wrote:
> 
> My use case is an abstract class. In Objective-C I used associated values on 
> the dynamic class object, and I had come to think this was relatively common. 
> I guess not.
> 
> On Wed, Aug 9, 2017 at 12:01 PM, Charlie Monroe  > wrote:
> Hi,
> 
> can you provide a usecase for this? I remember this being used in ObjC for 
> +version, but I'm not sure anymore where I'd use this...
> 
> BTW you don't need to stringify, use ObjectIdentifier (part of stdlib).
> 
> > On Aug 9, 2017, at 12:54 PM, Mathew Huusko V via swift-evolution 
> > mailto:swift-evolution@swift.org>> wrote:
> >
> > Curious if class stored properties have ever been discussed (doesn't seem 
> > so..)?
> >
> > Also, assuming no, and assuming there's a good reason no/they're not coming 
> > anytime soon, what are some patterns people have been using in their place? 
> > I was considering something like..
> >
> > class SomeClass {
> > private static var _classValues = [SomeClass.Type: Int]()
> >
> > class var value: Int {
> > get { _classValues[self] }
> > set { _classValues[self] = newValue }
> > }
> > }
> >
> > .. but then I remembered types aren't hashable yet either (so I guess I 
> > need to stringify it first).
> > ___
> > swift-evolution mailing list
> > swift-evolution@swift.org 
> > https://lists.swift.org/mailman/listinfo/swift-evolution 
> > 
> 
> 

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Re: [swift-evolution] [discussion] Class stored properties?

[Charlie Monroe via swift-evolution]

Hi,

can you provide a usecase for this? I remember this being used in ObjC for 
+version, but I'm not sure anymore where I'd use this...

BTW you don't need to stringify, use ObjectIdentifier (part of stdlib).

> On Aug 9, 2017, at 12:54 PM, Mathew Huusko V via swift-evolution 
>  wrote:
> 
> Curious if class stored properties have ever been discussed (doesn't seem 
> so..)?
> 
> Also, assuming no, and assuming there's a good reason no/they're not coming 
> anytime soon, what are some patterns people have been using in their place? I 
> was considering something like..
> 
> class SomeClass {
> private static var _classValues = [SomeClass.Type: Int]()
> 
> class var value: Int {
> get { _classValues[self] }
> set { _classValues[self] = newValue }
> }
> }
> 
> .. but then I remembered types aren't hashable yet either (so I guess I need 
> to stringify it first).
> ___
> swift-evolution mailing list
> swift-evolution@swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

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[swift-evolution] [discussion] Class stored properties?

[Mathew Huusko V via swift-evolution]

Curious if class stored properties have ever been discussed (doesn't seem
so..)?

Also, assuming no, and assuming there's a good reason no/they're not coming
anytime soon, what are some patterns people have been using in their place?
I was considering something like..

class SomeClass {
private static var _classValues = [SomeClass.Type: Int]()

class var value: Int {
get { _classValues[self] }
set { _classValues[self] = newValue }
}
}

.. but then I remembered types aren't hashable yet either (so I guess I
need to stringify it first).
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