3 ms·

A business method on order would do the same without any unnecessary overhead and ensuring proper encapsulation and consistency of the state that cannot be achi

A business method on order would do the same without any unnecessary overhead and ensuring proper encapsulation and consistency of the state that cannot be achieved with getters and setters. pendingOrders.map(order -> order.approvalConfirmationUpdated(now())

kitd 4y ago
I believe the intention is to allow operations on multilayered business objects to be composable. So your approvalConfirmationUpdated() method may actually be made up of a sequence of smaller operations, each of which I might want to use elsewhere in the application. Lenses allow this to happen succinctly, and works better with eg the Java streams API.
- ivan_gammel 4y ago
  I got that, my point is that such composability is rarely better than good old OOP with encapsulation. Enumerating all possible state transitions on object interface leads to better design than procedural programming (and composable operations are procedural programming).
ImprobableTruth 4y ago
I don't think I understand. We're talking about how to implement this. That method will still have to use deep copying + mutation, lenses or something else internally.
- ivan_gammel 4y ago
  You do not need lenses for implementation of a method working with internal state, that will be a gross over-engineering. record Order(List<Approval> approvals, int version, OrderStatus status) { Order confirmed(Instant timestamp, UUID approver) { var approvals = this.approvals.stream().map(a-> a.user().uuid().equals(approver) ? a.confirmed(timestamp) : a).toList(); return new Order(approvals, version++, OrderStatus.APPROVED); }
  - ImprobableTruth 4y ago
    Lenses are an abstraction of what you mentioned. For a single example it's of course overengineering. The benefit is that e.g. when you have a bunch of methods like that, you can avoid duplicating the code that is responsible for copying the inner layers. Otherwise if you e.g. add a layer, you have to touch all those methods.
    - ivan_gammel 4y ago
      If you look at my example you will notice that it has zero lines that would be duplicated in real life scenarios, because it does not perform a deep copy (a benefit of using immutable objects).
      - ImprobableTruth 4y ago
        Imagine you changed it from an array of approvals to a single one like in the original example - you'd need to make a change in every method of that type (replacing the map). That's code duplication, it's just not really obvious yet because there's only two layers to pass through. Per layer you need a constructor call (or map to copy & modify the array). As a more obvious example, if you want to modify a.b.c.d.e (which isn't unrealistic), you'll need to call the constructors of A, B, C and D. If you don't use lenses, this is the code that will be duplicated. You can spread it between the classes or do all that in a method of A, but if you want to also modify a.b.c.d.f, you'll need to duplicate all that code (add another method to A, B, C, D that each calls the constructor). With lenses, you define once how to access d from a and then any modification of d can happen through that. If the structure changes, you only need to do the changes once by modifying the lens.
        ivan_gammel 4y ago
        Those things are easy to imagine, however: 1) change in cardinality is such a change in domain that lenses won’t solve it. There will be much bigger changes in business logic probably making original code obsolete regardless of used pattern. 2) deep tree modifications of the kind that you mentioned indicate problems with architecture. Why would you need the whole typed tree (not DOM or something, but object tree) to modify a tiny leaf of it? If you touch multiple leafs with root as closest integration point, why your data model is designed like that, pointing to strong coupling of different contexts? 3) most importantly the code that can be reused, can be extracted to a private method of an entity where the change occurs. Calling nested constructors on the root object breaks encapsulation — it should pass the message to nested objects instead.

kitd 4y ago

I believe the intention is to allow operations on multilayered business objects to be composable. So your approvalConfirmationUpdated() method may actually be made up of a sequence of smaller operations, each of which I might want to use elsewhere in the application. Lenses allow this to happen succinctly, and works better with eg the Java streams API.

ivan_gammel 4y ago
I got that, my point is that such composability is rarely better than good old OOP with encapsulation. Enumerating all possible state transitions on object interface leads to better design than procedural programming (and composable operations are procedural programming).

ImprobableTruth 4y ago

I don't think I understand. We're talking about how to implement this. That method will still have to use deep copying + mutation, lenses or something else internally.

ivan_gammel 4y ago
You do not need lenses for implementation of a method working with internal state, that will be a gross over-engineering. record Order(List<Approval> approvals, int version, OrderStatus status) { Order confirmed(Instant timestamp, UUID approver) { var approvals = this.approvals.stream().map(a-> a.user().uuid().equals(approver) ? a.confirmed(timestamp) : a).toList(); return new Order(approvals, version++, OrderStatus.APPROVED); }
- ImprobableTruth 4y ago
  Lenses are an abstraction of what you mentioned. For a single example it's of course overengineering. The benefit is that e.g. when you have a bunch of methods like that, you can avoid duplicating the code that is responsible for copying the inner layers. Otherwise if you e.g. add a layer, you have to touch all those methods.
  - ivan_gammel 4y ago
    If you look at my example you will notice that it has zero lines that would be duplicated in real life scenarios, because it does not perform a deep copy (a benefit of using immutable objects).
    - ImprobableTruth 4y ago
      Imagine you changed it from an array of approvals to a single one like in the original example - you'd need to make a change in every method of that type (replacing the map). That's code duplication, it's just not really obvious yet because there's only two layers to pass through. Per layer you need a constructor call (or map to copy & modify the array). As a more obvious example, if you want to modify a.b.c.d.e (which isn't unrealistic), you'll need to call the constructors of A, B, C and D. If you don't use lenses, this is the code that will be duplicated. You can spread it between the classes or do all that in a method of A, but if you want to also modify a.b.c.d.f, you'll need to duplicate all that code (add another method to A, B, C, D that each calls the constructor). With lenses, you define once how to access d from a and then any modification of d can happen through that. If the structure changes, you only need to do the changes once by modifying the lens.
      - ivan_gammel 4y ago
        Those things are easy to imagine, however: 1) change in cardinality is such a change in domain that lenses won’t solve it. There will be much bigger changes in business logic probably making original code obsolete regardless of used pattern. 2) deep tree modifications of the kind that you mentioned indicate problems with architecture. Why would you need the whole typed tree (not DOM or something, but object tree) to modify a tiny leaf of it? If you touch multiple leafs with root as closest integration point, why your data model is designed like that, pointing to strong coupling of different contexts? 3) most importantly the code that can be reused, can be extracted to a private method of an entity where the change occurs. Calling nested constructors on the root object breaks encapsulation — it should pass the message to nested objects instead.