thoughts on C++ access modifiers

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liquidex 2023-09-07 16:26:24 +02:00
parent f8ca16a50d
commit 66eef2996f
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% id = "programming/projects" % id = "programming/projects"
+ ## projects + ## projects
- (actually nothing here yet lol, I was about to write something here but forgot but now don't wanna delete a branch I'm gonna bring back again anyways)
% content.link = "programming/cxx"
id = "programming/cxx"
+ ## C++
% content.link = "programming/unreal-engine" % content.link = "programming/unreal-engine"
id = "programming/unreal-engine" id = "programming/unreal-engine"
+ ## Unreal Engine + ## Unreal Engine

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- design lessons from the best programming language of all time that everyone loves (not really)
+ access modifiers as labels (`private:`, `protected:`, and `public:`)
- although Java and C#'s approach to symbol privacy may be verbose, it has one great advantage: it is stateless.
- the way they're implemented in C++, it's essentially a bit more parsing state you have to keep track of
- and you know what other parsing state you have to keep track of in C++? - that's right, the preprocessor.\
access modifiers, like all tokens, are affected by the preprocessor, and you have to take that into account
- take the following example:
```cpp
class ComfyZone
{
std::vector<SoftBed> _soft_beds;
#if ENABLE_HUGS
public:
void hug(Person& person);
#endif
int _remaining_hugs = 10;
};
```
- although quite contrived, it illustrates the problem pretty well
- (before you ask, `_remaining_hugs` needs to be always present because it has to be (de)serialized no matter if hugging functionality is compiled in. otherwise we'd get data loss.)
- we intended for `_remaining_hugs` to be private, but if hugs are enabled, it becomes public.
- this can be _very_ hard to spot if you have a big class with lots of declarations inside.
- this can be worked around by banning access modifiers from appearing in `#ifdef`s, but you have to *realize* that this might happen
- and I've seen instances of this exact thing occurring in the Unreal Engine codebase, which is *full* of long lists of declarations (made even longer by the prevalence of `UPROPERTY()`s)
- even if we didn't have the preprocessor, that access modifier is state _you_ have to keep track of
- I very often find myself needing to scroll upward after <kbd>Ctrl</kbd>-clicking on a field or function declaration, just to find out if I can use it
- (thankfully IDEs are helpful here and Rider shows you a symbol's visibility in the tooltip on hover, but I don't have Rider on code reviews)