Q:

Why am i getting this error while using Regex string from a .plist file?

When i am obtaining regex stored in a .plist file and supplying it to NSPredicate it is giving me an error. What basic concept of programming i am missing here ?
Previously i was using a regex like the following
static let PASSWORD_REGEX: String = "^[a-zA-Z_0-9\\-#!$@~`%&*()_+=|\"\':;?/>.<,]{6,15}$"

And supplying it for pattern match like this. and it was working fine.
func isValidPassword() -> Bool {

    let passwordRegex = Constants.PASSWORD_REGEX
    let passwordTest = NSPredicate(format: "SELF MATCHES %@", passwordRegex)
    let rVal = passwordTest.evaluate(with: self)
    return rVal
}

What have i changed is, i have moved this regex string to a .plist file and i am obtaining it from there. :-
static let PASSWORD_REGEX: String = Constants.getCustomizableParameter(forKey: "PASSWORD_REGEX")

static func getCustomizableParameter(forKey: String) -> String {
    var customizableParameters: NSDictionary?
    if let customizableParametersPlistPath = Bundle.main.path(forResource: "CustomizableParameters", ofType: "plist") {
        customizableParameters = NSDictionary(contentsOfFile: customizableParametersPlistPath)
    }
    if customizableParameters != nil {
        return customizableParameters![forKey] as! String
    } else {
        return ""
    }
}

And values in my plist are as follows :- 

Now when i am using the same password validation function. it is giving me following error :- 
Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Can't do regex matching, reason: Can't open pattern U_REGEX_INVALID_RANGE (string asdasd, pattern ^[a-zA-Z_0-9\\-#!$@~`%&*()_+=|\"\':;?/>.<,]{6,15}$, case 0, canon 0)'

A:

In a literal string in code you have to escape characters (e.g. \" instead of simple ").
In plist there is no such need. The \ characters will stay there, making your pattern invalid.
Remove the additional \ chars and everything will start to work.
Compare:
let PASSWORD_REGEX: String = "^[a-zA-Z_0-9\\-#!$@~`%&*()_+=|\"\':;?/>.<,]{6,15}$"
print(PASSWORD_REGEX)

outputs:
^[a-zA-Z_0-9\-#!$@~`%&*()_+=|"':;?/>.<,]{6,15}$

Which is the correct regular expression

