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  • If I want to extend 1 more subclass ToughGuy that only can temporary delete Account by setting status to "Temp_Closed", I have to use a lot of if/else in Account class. It violates O principle in SOLID. So, that is still fine ? Commented Jul 31, 2019 at 11:35
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    @NguyenNguyen: I don't subscribe to the strict interpretation of the Open/Closed principle that code must not ever be changed. If requirements change, like adding the feature of temporary deletion, then in my book it is fine to change existing code, as long as you can prove that you didn't break existing functionality that should still work. Commented Jul 31, 2019 at 12:40
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    @NguyenNguyen: You cannot close against any type of change; the Open/Closed principle must be applied strategically, where it matters - meaning against certain kinds of change, at certain parts of the codebase. If it turns out you made the wrong choices, then you have to redesign at some point. Which is why you want to postpone those choices until the "last responsible moment", when you know enough about the domain and the kinds of changes that are likely to occur, so that you can base the tradeoffs in your design around that knowledge. These principles must not be applied dogmatically. Commented Jul 31, 2019 at 15:54