foo.swift

let dict = UserDefaults.standard.dictionary(forKey: String(key)) ?? [:]
var result = Dictionary<Int,Bool>(minimumCapacity: dict.count)
for (key, value) in dict {
    guard let intKey = key as? Int,
        let boolValue = value as? Bool
        else { continue }
    result[intKey] = boolValue
}
return result