3 ms·

Well, I am a very strong proponent of keeping the hierarchy open in all possible cases; the object should be the one that defines the behavior in all cases, and

Well, I am a very strong proponent of keeping the hierarchy open in all possible cases; the object should be the one that defines the behavior in all cases, and an object's behavior shouldn't be restricted just because it comes from outside of the object or within. Therefore I agree with your point here.

9diov 3y ago
There are cases when the OOP way clearly has the disadvantage. That's why you need visitor pattern (https://en.wikipedia.org/wiki/Visitor_pattern?useskin=vector https://en.wikipedia.org/wiki/Visitor_pattern?useskin=vector). The ADT approach is superior in those cases, as stated in the link above.
- trashburger 3y ago
  Are you talking about the specific case in the expression problem article? It seems to mainly be a problem when an object's behavior can't be modified, either through the language faculties or through other means like a module system. I don't disagree with its conclusions but I believe it to be a problem of language capabilities.
- munificent 3y ago
  There are cases when the FP way clearly has the disadvantage. That's why you need the "record-of-function-pointers" pattern. The interface-and-implementations approach is superior in those cases.
  - 9diov 3y ago
    Haha lovely, clearly we are in agreement here. You even put that in your book isn't it? > The Visitor pattern is really about approximating the functional style within an OOP language (source: https://craftinginterpreters.com/representing-code.html https://craftinginterpreters.com/representing-code.html) The expression problem is one of those "mathematical duality" or yin-yang thing in software design that are less well-known for some reason. People keep pointlessly arguing in favor of one or another without knowing this duality. Another favorite of mine is SQL vs NoSQL which Erik Meijer mathematically proved to be dual of each other using category theory (https://queue.acm.org/detail.cfm?id=1961297 https://queue.acm.org/detail.cfm?id=1961297).
- igouy 3y ago
  Maybe we'd all be happier with multi-methods https://nice.sourceforge.net/visitor.html https://nice.sourceforge.net/visitor.html
_old_dude_ 3y ago
Closing the hierarchy or not depend on the use cases, for an application most hierarchies are closed. For a library most are open. For example, if your application receive JSON objects, you know all of them so, it's a closed hierarchy.

9diov 3y ago

There are cases when the OOP way clearly has the disadvantage. That's why you need visitor pattern (https://en.wikipedia.org/wiki/Visitor_pattern?useskin=vector https://en.wikipedia.org/wiki/Visitor_pattern?useskin=vector). The ADT approach is superior in those cases, as stated in the link above.

trashburger 3y ago
Are you talking about the specific case in the expression problem article? It seems to mainly be a problem when an object's behavior can't be modified, either through the language faculties or through other means like a module system. I don't disagree with its conclusions but I believe it to be a problem of language capabilities.
munificent 3y ago
There are cases when the FP way clearly has the disadvantage. That's why you need the "record-of-function-pointers" pattern. The interface-and-implementations approach is superior in those cases.
- 9diov 3y ago
  Haha lovely, clearly we are in agreement here. You even put that in your book isn't it? > The Visitor pattern is really about approximating the functional style within an OOP language (source: https://craftinginterpreters.com/representing-code.html https://craftinginterpreters.com/representing-code.html) The expression problem is one of those "mathematical duality" or yin-yang thing in software design that are less well-known for some reason. People keep pointlessly arguing in favor of one or another without knowing this duality. Another favorite of mine is SQL vs NoSQL which Erik Meijer mathematically proved to be dual of each other using category theory (https://queue.acm.org/detail.cfm?id=1961297 https://queue.acm.org/detail.cfm?id=1961297).
igouy 3y ago
Maybe we'd all be happier with multi-methods https://nice.sourceforge.net/visitor.html https://nice.sourceforge.net/visitor.html

_old_dude_ 3y ago

Closing the hierarchy or not depend on the use cases, for an application most hierarchies are closed. For a library most are open. For example, if your application receive JSON objects, you know all of them so, it's a closed hierarchy.