CODEWITHSUNDEEP
iosswift
user842225
user842225

Reputation: 5979

Cannot assign a value of type 'nil' to a value of type 'NSMutableArray'

I am writing swift code & having a simple problem.

I declared a MSMutableArray, under certain condition, I set it to nil:

 func doJob() -> NSMutableArray {
    var arr = NSMutableArray()
    arr = addContentToArray()
    if CRITICAL_CONDITION {
       //ERROR: Cannot assign a value of type 'nil' to a value of type 'NSMutableArray'
       arr = nil
    }
    return arr
}

But when I set arr to nil, I got compiler error:

Cannot assign a value of type 'nil' to a value of type 'NSMutableArray'

Why? How can I set it to nil then?

Upvotes: 0

Views: 1484

Answers (1)

Sulthan
Sulthan

Reputation: 130092

You can assign nil only to optional variables. However, when you are letting the type to be inferred, the compiler doesn't know that you are planning to assign nil in the future:

var arr: NSMutableArray? = NSMutableArray()

However, the whole thing about assigning nil to a variable that has previously held an array seems a bit dirty to me. Maybe it would be easier to use a new variable?

You haven't posted your real code so we can't do a real review but:

if CRITICAL_CONDITION {
   arr = nil
}

return arr

can be more easily written as

if CRITICAL_CONDITION {
   return nil
}

return arr

That will solve the problem, too, because you won't need to reassign the variable. A different approach would be to use a second variable:

var result: NSArray? = array
if CRITICAL_CONDITION {
   result = nil
}

return result

or even better

let result = CRITICAL_CONDITION ? nil: array
return result;

The whole point of specifying when a variable cannot be nil (non-optional) is the fact that optional variables are dangerous and you have to check them for nil all the time. So, use optionals only for a short time, ideally one condition and then convert them to non-optional. In this case, use the non-optional as long as possible and only when you really need to assign nil, convert to optional (declare a second, optional variable).

Upvotes: 3

Related Questions