Question: I have done some research on line and noticed that the apps you write in apple swift language would be working on OS X 10.9 and higher only. 

In order to make apps that work on earlier versions of OS X like 10.6 you would have to write them in objective C.

[Here](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/BuildingCocoaApps/MixandMatch.html#//apple_ref/doc/uid/TP40014216-CH10-XID_77) this apple document shows that you can write an app with a mix of both Swift and Objective C. I was wondering if anyone has been working in a similar project and if so, how have you gone with deciding what part to be coded in Swift and what part in objective C to make the app run on earlier versions of OS x? 

In other words, what part makes the swift language not to be working on earlier versions of OS X? I want to minimize the use of the objective C in an app and use Swift mostly and at the same time be able to run the app on earlier versions of OS X as well.

Any ideas and in put would be highly appreciated.

Answer: 
If you want it to run on an earlier version of OSX, then just have to write it in Objective-C.

You need to bundle a run-time library with swift code, and this library will not work correctly on releases earlier than 10.9 and usually crashes.

In addition, if you try to target an earlier release of OSX with your swift code, it will refuse to compile.
According to Apple Swift blog, Mavericks is the lowest [compatible](https://developer.apple.com/swift/blog/?id=2) version:

> 
> Simply put, if you write a Swift app today and submit it to the App Store this Fall when iOS 8 and OS X Yosemite are released, you can trust that your app will work well into the future. 
>  In fact, you can target back to OS X Mavericks or iOS 7 with that same app.
> 
> 
>