Is this self-initializing variable initialized at app launch, or initialized when it is first called upon by an executing code?

Question

Created Jul ’22

Replies 1

Boosts 0

Participants 2

What is this type of variable (specifically constant) declaration called that initializes itself with a "stored procedure" with code within curly braces followed by an empty set of parentheses? I don't know what key words to search for.

let object: NSObject = {
  let nestedObject = NSObject()
  return nestedObject
}()

I want to know if that variable gets initialized when it's needed the first time if I declare it globally in a swift file outside any other scope, or if it is initialized when the iOS app starts up before the variable is even called.

I thought the code within the curly braces runs when the iOS app launches, thus initializing the value of the variable, but I got an run time error while debugging my Xcode project when such a variable is called for the first time. I got a runtime error that says:

EXC_BREAKPOINT (code=1, subcode=0x...)

I also was told at one time in a question I posted on stackoverflow that the code runs only once.

Boost

Answer 1

Claude31 OP

Jul ’22

Where it it declared ? In a class ? Inside a func ?

If in a class, it should be executed when class is instantiated. If in a func, when func is called.

To understand better what happens, add a log:

let object: NSObject = {
  let nestedObject = NSObject()
  print("nestedObject created") 
  return nestedObject
}()

0