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

[Félix Cloutier]

Won't it be a concern with a cross-platform Swift?

Félix

> Le 3 févr. 2016 à 15:47:15, Douglas Gregor via swift-evolution <swift-evolution at swift.org> a écrit :
> 
>> 
>> On Feb 3, 2016, at 5:10 AM, Jean-Daniel Dupas via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> Using function availability has proven fragile in the past too. A function may be present but private on older system, and have a slightly different behavior or crash, and so should not be used.
> 
> This is a failing of the -respondsToSelector: idiom for checking availability. Swift’s #available feature checks the actual OS version, so it doesn’t suffer from this problem.
> 
> 	- Doug
> 
>> 
>> 
>>> Le 2 févr. 2016 à 11:03, James Campbell via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> a écrit :
>>> 
>>> 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>
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>>> 
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>>> 
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>> 
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