[swift-evolution] Pitch: really_is and really_as operators

[Adrian Zubarev]

Tested with Swift 3.0 Xcode 8 beta 6 playground.



-- 
Adrian Zubarev
Sent with Airmail

Am 25. August 2016 um 23:15:24, Vladimir.S (svabox at gmail.com) schrieb:

> let fooIsNSString = foo is NSString // true  

I don't understand. Why is so? On which version of Swift did you try this?  

IBM Swift Sandbox  
Swift Ver. 3.0 (Aug 23, 2016)  
Platform: Linux (x86_64)  

import Foundation  

let foo: Any = "Foo"  
let bar: Any = NSString(string: "Bar")  

let fooIsString = foo is String  
print(fooIsString) // true  

let fooIsNSString = foo is NSString  
print(fooIsNSString) // false! as expected  



On 25.08.2016 22:40, Adrian Zubarev via swift-evolution wrote:  
> Is that what you guys wanted to achieve?  
>  
> |@inline(never) func opaqueCast<T,U>(_ x: T, _: U.Type) -> Bool { return x  
> is U } let foo: Any = "Foo" let bar: Any = NSString(string: "Bar") let  
> fooIsString = foo is String // true opaqueCast(type(of: foo),  
> String.Type.self) // true let fooIsNSString = foo is NSString // true  
> opaqueCast(type(of: foo), NSString.Type.self) // false let barIsString =  
> bar is String // true opaqueCast(type(of: bar), String.Type.self) // false  
> let barIsNSString = bar is NSString // true opaqueCast(type(of: bar),  
> NSString.Type.self) // true |  
>  
> Joe Groff showed me this little trick when |is| cast was bugged in some  
> Xcode beta for Swift 1.2.  
>  
>  
>  
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> swift-evolution at swift.org  
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>  
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