How can I call `didSet` method using `Codable` protocol - swift

Question

How can I call didSet method using Codable protocol.
class Sample: Codable{
var text : String? {
didSet {
print("didSet") // do not call
extended_text = "***" + text! + "***"
}
}
var extended_text : String?
}
let sample_json = "{\"text\":\"sample text\"}"
let decoder = JSONDecoder()
let sample = try! decoder.decode(Sample.self, from: sample_json.data(using: .utf8)!)
print(sample.text!)
print(sample.extended_text ?? "")

Answer 1

Instead of using didSet you should just make extendedText a read only computed property. Note that it is Swift convention to use camelCase instead of snake_case when naming your properties:
struct Sample: Codable {
let text: String
var extendedText: String {
return "***" + text + "***"
}
}
let sampleJson = """
{"text":"sample text"}
"""
do {
let sample = try JSONDecoder().decode(Sample.self, from: Data(sampleJson.utf8))
print(sample.text) // "sample text\n"
print(sample.extendedText) // "***sample text***\n"
} catch {
print(error)
}
An alternative if your goal is to run a method when initializing your Codable struct is to write your own custom decoder:
class Sample: Codable {
let text: String
required init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
text = try container.decode(String.self)
print("did set")
}
}
let sampleJson = "{\"text\":\"sample text\"}"
let decoder = JSONDecoder()
do {
let sample = try decoder.decode([String: Sample].self, from: Data(sampleJson.utf8))
print(sample["text"]?.text ?? "")
} catch {
print(error)
}
This will print:
did set
sample text