Recursively change some keys in a Dictionary in Swift - swift

Question

I have a dictionary
var dictionary: Any = ["det" : ["val" : "some","result" : ["key1" : "val1","key2" : "val2"],"key3" :["val1", "val2"]]]
and a mapping function below
func getMappedKey(_ key: String) -> String? {
var mapping: Dictionary = [
"key1" : "key3",
"key2" : "key4",
"det" : "data"
]
return mapping[key]
}
Now I want to change some keys in the same dictionary using the mapping function above. So after the change, the dictionary should look like
["data" : ["val" : "some","result" : ["key3" : "val1","key4" : "val2"],"key3" :["val1", "val2"]]]
So for that I wrote a function below
func translatePayload(_ payload: inout Any) {
if let _ = payload as? String {
return
} else if var payload = payload as? Dictionary<String, Any> {
for (key, value) in payload {
if let newKey = getMappedKey(key) {
if let _ = payload.removeValue(forKey: key) {
payload[newKey] = value
}
}
var nextPayload = value
translatePayload(&nextPayload)
}
} else if let payload = payload as? Array<Any> {
for value in payload {
var nextPayload = value
translatePayload(&nextPayload)
}
}
}
and when I call the function
translatePayload(&dictionary)
print(dictionary)
it does not change the keys in the same dictionary. Can someone please point out what is wrong with this code. Thanks in advance

Answer 1

Your code is perfectly fine, you just updated the local variable instead of the parametric one because you used the same name. Just change the local variable payload to dictionary and array or anything else you like.
Here is the final code:
func translatePayload(_ payload: inout Any) {
if let _ = payload as? String {
return
} else if var dictionary = payload as? Dictionary<String, Any> { // Here dictionary instead of payload
for (key, value) in dictionary {
var nextPayload = value
translatePayload(&nextPayload)
if let newKey = getMappedKey(key) {
if let _ = dictionary.removeValue(forKey: key) {
dictionary[newKey] = nextPayload
}
} else {
dictionary[key] = nextPayload
}
}
payload = dictionary
} else if let array = payload as? Array<Any> { // Here array instead of payload
var updatedArray = array
for (index, value) in array.enumerated() {
var nextPayload = value
translatePayload(&nextPayload)
updatedArray[index] = nextPayload
}
payload = updatedArray // Assign the new changes
}
}
translatePayload(&dictionary)
print(dictionary)

Answer 2

Not really a direct answer to the question "what's wrong", but I'd go with something like:
let dictionary = ["det" : ["val" : "some","result" : ["key1" : "val1", "key2" : "val2"],"key3" :["val1", "val2"]]]
func getMapped(key: String) -> String {
var mapping: Dictionary = [
"key1" : "key3",
"key2" : "key4",
"det" : "data"
]
return mapping[key] ?? key
}
func translate(payload:Any, map:(String)->String) -> Any {
switch payload {
case let value as String:
return value
case let value as [String:Any]:
return value.reduce(into:[String:Any]()) {
$0[map($1.0)] = translate(payload: $1.1, map:map)
}
case let value as [Any]:
return value.map { translate(payload: $0, map:map) }
default:
fatalError("Unknown data type")
}
}
let output = translate(payload: dictionary, map:getMapped(key:))
To really take advantage of the functional spirit of Swift.