How to safely unwrap a value from user defaults?

Question

if let seen: Bool = defaults.bool(forKey: UtilitiesKeys.mainTutorialSeen) {
    return seen
}
return false

if i do this swift shows me an issue:

Conditional cast from 'Bool' to 'Bool' always succeeds, Non-optional expression of type 'Bool' used in a check for optionals.

Since there might not be a value for my key, I don't want to force unwrap it. Now obviously it's working like this, but how do I safely unwrap the value without having swift complaining?

I have tried to use guard as well...

Hmm, displays the same issue but d0ye's answer works. Still thanks though :) — Lorenz Saalmann, Dec 20 '17 at 06:47

score 2 · Answer 1 · answered Dec 20 '17 at 06:41

2

if let seen = UserDefaults.standard.object(forKey: UtilitiesKeys.mainTutorialSeen)) as? Bool {
        return seen
    }else {
        return false
    }

answered Dec 20 '17 at 06:41

d0ye

1,580
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Please provide some context or an explanation of how this code solves the problem. This will make it more useful for more readers. – Brett DeWoody Dec 22 '17 at 05:16
can u provide guard let? – kemdo Jul 26 '18 at 03:17

score 1 · Answer 2 · answered Dec 20 '17 at 06:45

Apple document says:

/*! -boolForKey: is equivalent to -objectForKey:, except that it converts the returned value to a BOOL. If the value is an NSNumber, NO will be returned if the value is 0, YES otherwise. If the value is an NSString, values of "YES" or "1" will return YES, and values of "NO", "0", or any other string will return NO. If the value is absent or can't be converted to a BOOL, NO will be returned.

open func bool(forKey defaultName: String) -> Bool

Initializer for conditional binding must have Optional type, not 'Bool'

hope this help you.

Dharmesh Kheni · Accepted Answer · 2017-12-20T06:58:02.267

As suggested in doc:

-boolForKey: is equivalent to -objectForKey:, except that it converts the returned value to a BOOL. If the value is an NSNumber, NO will be returned if the value is 0, YES otherwise. If the value is an NSString, values of "YES" or "1" will return YES, and values of "NO", "0", or any other string will return NO. If the value is absent or can't be converted to a BOOL, NO will be returned.

open func bool(forKey defaultName: String) -> Bool

It is not an optional anymore. So you don't need to cast it with if let.

You can directly use:

let seen = defaults.bool(forKey: UtilitiesKeys.mainTutorialSeen)

Ah yeah, thanks, might as well do that since its the shortest way of doing it. — Lorenz Saalmann, Dec 22 '17 at 04:01

How to safely unwrap a value from user defaults?

3 Answers3