In this gist I will show you how to use custom keyDecodingStrategy/keyEncodingStrategy in new Codable/Decodable protocols in swift 4.1 with a simple example.

Persons.swift

let json = """
[
{
"first-Name": "Taylor",
"last-Name": "swift",
"age": 28
},
{
"first-Name": "Tom",
"last-Name": "hanks",
"age": 61
}
]
"""

struct Person: Codable {
	var firstName: String
	var lastName: String
	var age: Int
}

struct PersonKey: CodingKey {
	var stringValue: String
	var intValue: Int?

	init?(stringValue: String) {
		self.stringValue = stringValue
		self.intValue = nil
	}

	init?(intValue: Int) {
		self.stringValue = String(intValue)
		self.intValue = intValue
	}
}

let jsonDecoder = JSONDecoder()
//here you set the strategy, could be .convertFromSnakeCase apart from .useDefaultKeys. So basically we dont need the `CodingKeys enumerations` anymore
jsonDecoder.keyDecodingStrategy = .custom { keys -> CodingKey in
	let key = keys.last!.stringValue.split(separator: "-").joined()
	return PersonKey(stringValue: String(key))!
}

do {
	let persons = try jsonDecoder.decode([Person].self, from: Data(json.utf8))
	print(persons)
} catch {
	print(error.localizedDescription)
}