Integer keys

[michelf]

This code adds an encoding and decoding mode where keys in the message pack data are allowed to be integer. If the provided key returns a non-nil intValue and allowIntKeys is set to true in the encoder/decoder, the integer key will be used instead of its string form.

[hirotakan]

If you change as follows, I think that Decoder does not need allowIntKeys.

        func contains(_ key: Key) -> Bool {
            if let intValue = key.intValue, let _ = container[.int(intValue)] {
                return true
            }
            return container[.string(key.stringValue)] != nil
        }

        func findEntry(by key: CodingKey) throws -> Data {
            if let intValue = key.intValue, let entry = container[.int(intValue)] {
                return entry
            }

            if let entry = self.container[.string(key.stringValue)] {
                return entry
            }

            let context = DecodingError.Context(codingPath: self.decoder.codingPath, debugDescription: "No value associated with key \(key) (\"\(key.stringValue)\").")
            throw DecodingError.keyNotFound(key, context)
        }

[hirotakan]

Thanks for a good idea!
But I want to change to:

1. Add KeyEncodingType.

public enum KeyEncodingType {
    case string
    case int
}

2. Change the initializer.

    private let keyEncodingType: KeyEncodingType

    public init(keyEncodingType: KeyEncodingType = .string) {
        self.keyEncodingType = keyEncodingType
    }

[michelf]

Sounds like a good idea.