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Auto-implement class/struct as envelope for top level arrays in JSON by implementing this simple protocol
protocol TopLevelCollection: Codable {
associatedtype ElementType: Codable
var elements: [ElementType] { get set }
init(elements: [ElementType])
extension TopLevelCollection {
public init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
var elements: [ElementType] = []
while !container.isAtEnd {
let subdecoder = try container.superDecoder()
let subcontainer = try subdecoder.singleValueContainer()
let element = try subcontainer.decode(ElementType.self)
self.init(elements: elements)
func encode(to encoder: Encoder) throws {
var container = encoder.unkeyedContainer()
try container.encode(contentsOf: elements)
/// USAGE:
struct Foo: TopLevelCollection {
var elements: [String]
// ["foo", "bar", "blah"] JSON will now be mapped to 'elements' and will be encoded back into the same format
struct Bar: TopLevelCollection {
var elements: [BarCodable]
struct BarCodable: Codable {
let name: String
/// [ { "name": "Jerry" }, { "name": "Bob" } ] will be mapped to 'Bar''s elements and vice-versa
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