Key decoding strategies for Codable 관련

HACKING WITH SWIFT

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What's new in Swift?

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Key decoding strategies for Codable | Changes in Swift 4.1

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Key decoding strategies for Codable

Available from Swift 4.1

In Swift 4.0 a common problem was trying to use Codable with JSON that utilized snake_case for its key names rather than the camelCase we normally use in Swift. Codable was unable to understand how the two different name types were mapped, so you had to create a custom CodingKeys enum helping it out.

This is where Swift 4.1's new keyDecodingStrategy property comes in: it’s set to .useDefaultKeys by default, which does a direct mapping of JSON names to Swift properties. However, if you change it to .convertFromSnakeCase then Codable handles the name conversion for us.

For example:

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase

do {
    let macs = try decoder.decode([Mac].self, from: jsonData)
    print(macs)
} catch {
    print(error.localizedDescription)
}

When you want to go back the other way – to convert a Codable struct with camelCase properties back to JSON with snake_case keys, set the keyEncodingStrategy to .convertToSnakeCase like this:

let encoder = JSONEncoder()
encoder.keyEncodingStrategy = .convertToSnakeCase
let encoded = try encoder.encode(someObject)

Note

At the time of writing keyDecodingStrategy and keyEncodingStrategy are not available on Linux.

Other Changes in Swift 4.1

Synthesized Equatable and Hashable | Changes in Swift 4.1

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Synthesized Equatable and Hashable

Conditional conformances | Changes in Swift 4.1

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Conditional conformances

Recursive constraints on associated types | Changes in Swift 4.1

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Recursive constraints on associated types

Build configuration import testing | Changes in Swift 4.1

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Build configuration import testing

Target environment testing | Changes in Swift 4.1

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Target environment testing

flatMap is now (partly) compactMap() | Changes in Swift 4.1

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flatMap is now (partly) compactMap()

Download Swift 4.1 playground