gistfile1.swift

import Himotoki

struct User: Decodable { ... }

struct Foo: Decodable {
    let name: String
    let users: [User]
    
    static func decode(e: Extractor) -> Foo? {
        let create = { Foo($0) }
        return build(
            e <| "name",
            (e <| "uesr").map { [$0] } ?? e <|| "users"
        ).map(create)
    }
}