Nil Swift Dictionary

Question

My dictionary is always nil, would like to understand why this is happening. My code:

var dic = [NSDate : MCACalendar]?()
dic?[currentDate!] = calendar

Answer 1

@Kirsteins provides the solution - but it's good to know why.

Using [NSDate : MCACalendar]?() doesn't work as you expect because it creates an instance of [NSDate : MCACalendar]? , ie an instance of an optional - to be more precise, an instance of Optional<[NSDate : MCACalendar]> . So that initialization doesn't create an instance of [NSDate : MCACalendar] .

Creating an instance of an optional ( Optional<T> ) using the parameterless constructor initializes it to .None (equivalent to nil ), so for example in:

var x = Int?() // `x` is initialized as `.None`

If a parameter is passed to the constructor, then the optional variable is initialized with .Some :

var x = Int?(5) // x is initialized as `.Some(5)`

That explains Kirsteins's solution no. 1. Solution no. 2 is so obvious that it doesn't need further explanation :)

Answer 2

It seems [NSDate : MCACalendar]?() fails and returns nil . You probably want to use:

var dic = [NSDate : MCACalendar]?([:])

or

var dic: [NSDate : MCACalendar]? = [:]