checkpoint.swift

class Checkpoint {
    /// ...
    
    var userInfo: [String: Codable] = [:]
}

protocol Checkpointable {
    init(checkpoint: Checkpoint)
    
    func read(from: Checkpoint)
    func write(to: Checkpoint)
}

// make it optional
extension Checkpointable {
    init(checkpoint: Checkpoint) { fatalError()}
}

struct Model: Checkpointable {


    let hiddenLayerFeatureChannels: Int
    
    init(hiddenLayerFeatureChannels: Int) {
        self.hiddenLayerFeatureChannels = hiddenLayerFeatureChannels
    }
    
    init(checkpoint: Checkpoint) {
        guard
            let hiddenLayerFeatureChannels = checkpoint.userInfo["ngf"] as? Int
        else { fatalError()}
        
        self.init(hiddenLayerFeatureChannels: hiddenLayerFeatureChannels)
        self.read(from: checkpoint)
    }
    
    func read(from: Checkpoint) {
        // Normal reading
    }
    
    func write(to checkpoint: Checkpoint) {
        // Normal writing
        
        checkpoint.userInfo["ngf"] = hiddenLayerFeatureChannels
    }
}