Open Radar

 
Summary:
The 'dynamicType' special keyword/property can be used to retrieve the runtime type of an object (as an AnyClass). The type can then be downcast using as? to produce a T.Type object, on which initializers and class methods can be called.

It's possible to construct a simple program which perform the above operation on an NSString, and then attempts to initialize a new NSString, and successfully compile this program. However, this program crashes when run because it cannot find the proper initializer to use.

Steps to Reproduce:
Run the sample project enclosed.

Expected Results:
Xcode produces an error when trying to compile the program, or program successfully compiles and runs and is able to use stringTypeValue() to instantiate a new NSString instance.

Actual Results:
Application crashes when trying to instantiate a new NSString instance (line 22), with the error message in the console: "/SourceCache/swiftlang/swiftlang-602.0.37.3/src/swift/stdlib/core/StringBridge.swift: 128: 20: fatal error: use of unimplemented initializer 'init()' for class 'Swift._NSContiguousString'"

Version:
Both Xcode 6.1 and 6.2 beta (6D520o), running on OS X Yosemite (10.10.2).

Notes:
I don't think this is isolated to NSStrings; I think it may be an issue for all Foundation bridged classes that are implemented using Objective-C class clusters.

Configuration:


Attachments:
'SwiftMetaclass.zip' was successfully uploaded.

Note: SwiftMetaclass's single source file is reproduced below in its entirety:

import Foundation

println("Hello, World!")

func classForObject(object: AnyObject) -> AnyClass {
    return object.dynamicType
}

let anyTypeValue : AnyClass = classForObject("hello world")

if let stringTypeValue = anyTypeValue as? NSString.Type {
    println("classForObject returned a NSString.Type")
    // Crashes here
    let newString = stringTypeValue()
}