Open Radar

 
Summary:
Swift2 guard expression crashes when subscript with unexisting key is called on AnyObject

Steps to Reproduce:
1. Start a new Swift2 project
2. Add a function to your ViewController:

    func willCrashWithObject(object: AnyObject) -> AnyObject? {
        
        guard let nested: AnyObject = object["unexisting_key"] else {
            return nil
        }
        
        return nested
        
    }

3. Add the following code to viewDidLoad method:

        let _ = willCrashWithObject(["a": 5])



Expected Results:
Function should return nil

Actual Results:
Code crashes with error: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)

Version:
iOs 9.0

Notes:
There are 3 ways to avoid an issue:
1) Remove AnyObject: 
guard let nested = object["unexisting_key"] else

2) Make it optional
guard let nested: AnyObject? = object["unexisting_key"] else

3) Pass dictionary to willCrashWithObject instead of AnyObject

Configuration:
iPhone5c