Codable and JSON

Codable and JSON

A type that conforms to Codable can be converted to and from JSON by JSONEncoder and JSONDecoder. For most structs the compiler writes the conversion for you. Use a CodingKeys enum to map names in the JSON to your property names, optionals for fields that may be missing, and a custom init(from:) when the shape of the JSON does not match your model. Options on the decoder handle date formats and naming styles.

One trap is worth remembering. The .convertFromSnakeCase option turns image_url into imageUrl, not imageURL, and a property named imageURL then quietly fails to decode. When decoding does fail, read the DecodingError: it names the exact key and the path to it.

Decode real JSON from a public API into structs. Make one field optional, and rename one with CodingKeys. Then break the JSON on purpose and read the error that results.

1. What does the compiler generate when you declare a struct Codable?
2. How do you map a JSON key price_cents to a property named priceCents?
3. What does a DecodingError tell you?

• Codable
• Encoding and decoding custom types