What happens to the value of the counter variable if it is included in the capture list and used inside a closure?

If a variable counter is included in the capture list of a closure in Swift, then inside this closure, a copy of the value of counter at the moment of the closure's creation will be used. This means that changes to counter outside the closure after its creation will not affect the value inside the closure.

However, if counter is a mutable object (for example, a class), then the closure will capture a reference to this object, and changes inside the closure will reflect on the object itself.

Example with a primitive type:

var counter = 0
let closure = { [counter] in
    print(counter) // will always print 0, even if counter changes later
}
counter = 10
closure() // will output 0

If you want the closure to modify and preserve changes to counter, you can use inout parameters or capture the variable without a capture list (by reference), for example, if it is a class.