Capturing a weak reference to self in a nested closure could cause a retain cycle. `[weak self]` weakly captures self from the outer closure. Since the outer closure did not declare a weak reference to self, it will keep a strong one.

NestedClosureWeakSelfRetainCycle.swift

class ViewModel {
    
    let intGetterGetter: () -> () -> Int?
    var currentInt = 2

    init() {
        self.intGetterGetter = {
            return { [weak self] in
                return self?.currentInt
            }
        }
    } 
}