Require either of two fields

[musjj]

Is there a way to require either of two fields in a config?

struct AppConfig {
    left: Option<String>,
    right: Option<String>,
}

Either left or right have to present (or both). I'm thinking of using enums, but I'm not sure how to make it work.

[epage]

You would need to handle this through writing a custom Deserialize in serde. You could do that by having a AppConfigInternal that derives Deserialize and your hand-implemented Deserialize would call that and add the error check.