swift_4_1_whats_new_json_snake_case.swift

struct Person: Codable {
    let firstName: String
    let lastName: String
}

let jsonData = """
{
    "first_name": "John",
    "last_name": "Watson"
}
""".data(using: .utf8)!

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let person = try! decoder.decode(Person.self, from: jsonData) // Person(firstName: "John", lastName: "Watson")