Marking it private doesn't allow any subclasses to change the value directly and must use the get/set methods provided where you can enforce standards or format accordingly.
Ask HN: Why do you make class members private?
11–20 of 117 posts
Re: Ask HN: Why do you make class members private?
#12Variables should not be accessed directly outside of the object (encapsulation principle) and thus should all be private as a general rule. Then, you will probably divide up the code into a number of separate methods for better structured code. All the methods that are purely internal and not part of the public API should be private if only to enforce the public API, this is also the encapsulation principle.
Python would like a word...
Re: Ask HN: Why do you make class members private?
#13To hide implementation details from class users. You ideally only want to have a documented interface and all implementation details should be opaque to class users. This can be quite tricky and usually classes will export some state, typically done through getters and setters.
Then one day you decide you want to aggressively refactor that class. Now you can because the interface can stay the same even though you could completely re-do the guts. Better still: all your tests will still work, as will your class documentation.
Re: Ask HN: Why do you make class members private?
#14I don’t want them to show up in auto complete and accidentally use them because its not my business, I should not use things that I shouldnt.
Re: Ask HN: Why do you make class members private?
#15We do it because that's how it's always been done. There is no why of OOP, there is only do.
Re: Ask HN: Why do you make class members private?
#16Because they are for the use of the functions within the class/module/whatever, not for the use of functions interfacing with it. Private functions for me are mainly for DRY, not for being secret special menu items.
Re: Ask HN: Why do you make class members private?
#17Variables should not be accessed directly outside of the object (encapsulation principle) and thus should all be private as a general rule. Then, you will probably divide up the code into a number of separate methods for better structured code. All the methods that are purely internal and not part of the public API should be private if only to enforce the public API, this is also the encapsulation principle.
Python would like a word...
While we're on Python and private methods - what's with everyone just _underscoring every method and variable by default? Does anyone teach people to do this or have I just ran into a few people with this habit by chance?
I know what _underscoring does in Python and what PEP8 recommends but doing it all the time for everything is so ugly and unnecessary.
Re: Ask HN: Why do you make class members private?
#18Because classes are encapsulated data plus contracts over managing the object's state. If a class does not have control of its own data, then it cannot fulfill its contracts.
Let's say I have a Motorcycle class with 2 Wheel members. What if in the code I assume 2 Wheels when writing the serializer? And then someone comes along, instantiates a Motorcycle and nukes a Wheel? The code will break.
You can make an argument that OOP is not what you want, and instead create something akin to namespaces+data, and that's fine. But OOP's thing is to create a public API, and controlled state behind it.
Re: Ask HN: Why do you make class members private?
#19Suppose all fields are public, but the legal value of a field is dependent upon others. Then every time you change it you also have to include all the invariant preserving logic. This is duplication of the insane sort, totally unnecessary and gratuitous and gloriously error prone (at scale). The sane option is to make it private and have one place that checks that the input is valid and have everything make use of that.
Re: Ask HN: Why do you make class members private?
#20Enforce invariants
I used to believe in information hiding, but not anymore.