[swift-evolution] #available has a huge anti-pattern.

[Joe Groff]

Polyfills have their own tradeoffs; they tend to encourage constant accretion of glue code as new versions get added if there's no pressure to drop old versions, leading to a significant amount of the multi-megabyte Javascript framework downloads we all complain about these days. That said, you might be able to use the related `@available` attribute to introduce backfill extensions that are only available on older systems.

-Joe

> On Feb 2, 2016, at 2:03 AM, James Campbell via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Coming from a web background (before my iOS career) to me #avaliable has huge problem. It encourages fragility.
> 
> In my eyes we should encourage two types of detection: Features to make code more adaptable to different environments and language version detection: so we can understand the actual code.
> 
> See this example below:
> 
> func magic(object: Object)
> {
>   if(#avaliable(9.0, 10))
>  {
>   object.foo()
>  }
> }
> 
> Ideally for me I would love to check if the foo function exists like so:
> 
> func iOS9OnlyProtocolFunction(object: Object)
> {
>   if(#avaliable(Object.foo))
>  {
>     object.foo()
>  }
> else 
> {
>   object.baz()
>  }
> }
> 
> I think this encourages feature detection which results in less fragile code. What I would love to do is also to extend this to extensions so we could encourage polyfills.
> 
> extend object where not_avaliable(Object.foo) 
> {
>   func foo() 
>  {
>    //Polyfill for platforms which don't support the Object.foo method
>  }
> }
> 
> Not sure about compiler details but being able to polyfill the function results in much cleaner code for me. I love this approach from the web, so I created my own Objective-C Library to do this:
> 
> https://github.com/jcampbell05/Polly <https://github.com/jcampbell05/Polly>
> ___________________________________
> 
> James⎥Lead Engineer
> 
> james at supmenow.com <mailto:james at supmenow.com>⎥supmenow.com <http://supmenow.com/>
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