playing with dynamicMemberLookup

find_by_dynamic.swift

class Database {
    private static let users = [User(id: 1, name: "Jane"), User(id: 2, name: "Clara"), User(id: 3, name: "Sandy")]
    
    static func find(id: Int) -> User? {
        return users.first(where: { $0.id == id })
    }
    
    static func find(name: String) -> User? {
        return users.first(where: { $0.name == name })
    }
}

@dynamicMemberLookup
public class Queryable<T> { }

extension Queryable where T == User.Type {
    public subscript(dynamicMember member: String) -> (Any) -> User? {
        return { arg in
            if let id = arg as? Int {
                return Database.find(id: id)
            } else if let name = arg as? String {
                return Database.find(name: name)
            } else {
                return nil
            }
        }
    }
}

public protocol QueryProviding { }

extension QueryProviding {
    public typealias QueryBase = Self.Type

    public static var query: Queryable<QueryBase> {
        return Queryable<QueryBase>()
    }
}

public struct User {
    public let id: Int
    public let name: String
}

extension User: QueryProviding { }

User.query.find_by_id(42)
User.query.find_by_name("Jane")
User.query.find_by_id(3)