scout VS BackedCodable

I developed a library that is better suited for such cases than plain Decodable. You can specify a path in the data and at the end of the path specify a Decodable type to be instantiated from the data.

Not 100% sure but you might find Scout interesting for your needs

I developed Scout for this exact purpose because I had to find a solution to get a value when the data structure is not known at build time.

If you are ok to use a program, you can use Scout like that: curl [your curl request here] | scout read -f xml "a-valid-date"

For a clear and simple syntax, you can take a look at Scout.

I have been working myself on Scout to work on data when the format is not known at build time (for instance with a generic command line tool). And I have never had the tuple decoding requested. Although this might be useful for some people.

From what I understand, you are not the only one trying those ideas. For instance BackedCodable uses property wrappers to use a custom strategy to decode a property. I myself had to implement a similar logic to decode a Plist configuration file where keys are sometime required only when another is not present. I similarly use property wrappers with mirroring.