Swift has a pair of protocols, Encodable and Decodable, which represent generic encoding of a tree structure. These protocols are special in that the compiler can provide a default implementation for them under many circumstances. Similarly, Rust has a project called Serde which likewise is used for roughly the same purpose; Serde’s traits are even more complicated than Codable’s, but have even more powerful code synthesis via Rust’s proc-macros. Both tools are very useful but occasionally frustrating, and I think some of the frustrating areas come from a tension between two competing use cases.

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