Confused about getAsNSString from bullet point 5, used again in bullet
point 8 — the function wont compile for me:
Check whether a value is _ObjectiveCBridgeable to a class, or conversely,
that an object is _ObjectiveCBridgeable to a value type, and perform the
bridging conversion if so:func getAsString<T>(value: T) -> String? {
return value as? String
}func getAsNSString<T>(value: T) -> NSString {
return value as? NSString
}getAsString(value: "string") // produces "string": String
getAsNSString(value: "string") // produces "string": NSString
let ns = NSString("nsstring")
getAsString(value: ns) // produces "nsstring": String
getAsNSString(value: ns) // produces "nsstring": NSString
Drill through Optionals. If an Optional contains some value, it is
extracted, and the cast is attempted on the contained value; the cast fails
if the source value is none and the result type is not optional:var x: String? = "optional string"
getAsNSString(value: x) // produces "optional string": NSString
x = nilgetAsNSString(value: x) // fails$ /Applications/Xcode-7D1010.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift
Welcome to Apple Swift version 2.2 (swiftlang-703.0.18.5
clang-703.0.31). Type :help for assistance.
1> import Foundation
2>
3> func getAsNSString<T>(value: T) -> NSString {
4. return value as? NSString
5. }
repl.swift:4:16: error: value of optional type 'NSString?' not
unwrapped; did you mean to use '!' or '?'?
return value as? NSString
^
( )!
3>
$ /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2016-04-12-a.xctoolchain/usr/bin/swift
Welcome to Apple Swift version 3.0-dev (LLVM 752e1430fc, Clang
3987718dae, Swift 36739f7b57). Type :help for assistance.
1> import Foundation
2>
3> func getAsNSString<T>(value: T) -> NSString {
4. return value as? NSString
5. }
error: repl.swift:4:16: error: value of optional type 'NSString?' not
unwrapped; did you mean to use '!' or '?'?
return value as? NSString
^
( )!
I would think the function was meant to end -> NSString?, if not for the //
fails comment in bullet 8. Could you clarify?
– J.D. Healy