main.swift

import Foundation

struct FailableDecodable<Base : Decodable> : Decodable {

  let base: Base?

  init(from decoder: Decoder) throws {
    let container = try decoder.singleValueContainer()
    self.base = try? container.decode(Base.self)
  }
}

struct FailableCodableArray<Element : Codable> : Codable {

  var elements: [Element]

  init(from decoder: Decoder) throws {

    var container = try decoder.unkeyedContainer()

    var elements = [Element]()
    if let count = container.count {
      elements.reserveCapacity(count)
    }

    while !container.isAtEnd {
      if let element = try container
        .decode(FailableDecodable<Element>.self).base {

        elements.append(element)
      }
    }

    self.elements = elements
  }

  func encode(to encoder: Encoder) throws {
    var container = encoder.singleValueContainer()
    try container.encode(elements)
  }
}

struct ProductsRoot : Codable {
  var products: [GroceryProduct]

  init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    self.products = try container
      .decode(FailableCodableArray<GroceryProduct>.self, forKey: .products)
      .elements
  }
}

// or...

struct ProductsRoot2 : Codable {

  private let _products: FailableCodableArray<GroceryProduct>
  var products: [GroceryProduct] {
    return _products.elements
  }

  private enum CodingKeys : String, CodingKey {
    case _products = "products"
  }
}

struct GroceryProduct : Codable {
  var name: String
  var points: Int
  var description: String?
}


let jsonString = """
{ "products": [
    {
        "name": "Banana",
        "points": 200,
        "description": "A banana grown in Ecuador."
    },
    {
        "name": "Orange"
    }
]}
"""

let jsonData = Data(jsonString.utf8)


do {
  let decoded = try JSONDecoder().decode(ProductsRoot.self, from: jsonData)
  print(decoded)

  let decoded2 = try JSONDecoder().decode(ProductsRoot2.self, from: jsonData)
  print(decoded2)
} catch {
  print(error)
}