57 lines
2.6 KiB
Plaintext
57 lines
2.6 KiB
Plaintext
|
%% title = "C++ syntactic pitfall: access modifiers as labels"
|
||
|
|
|
||
|
|
% id = "01H9R1KJES39Z6RBCKY4E71PYD"
|
||
|
|
- although Java and C#'s approach to symbol privacy may be verbose, it has one great advantage: it is stateless.
|
||
|
|
|
||
|
|
% id = "01H9R1KJES17626QXYEGM7XBC7"
|
||
|
|
- the way they're implemented in C++, it's essentially a bit more parsing state you have to keep track of
|
||
|
|
|
||
|
|
% id = "01H9R1KJESG4K8T1K1G36T7HBP"
|
||
|
|
- 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.
|
||
|
|
|
||
|
|
% id = "01H9R1KJESJ0G0VQAW994ZHR0S"
|
||
|
|
- 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;
|
||
|
|
};
|
||
|
|
```
|
||
|
|
|
||
|
|
% id = "01H9R1KJESDDX4089WVHVV8N3H"
|
||
|
|
+ although quite contrived, it illustrates the problem pretty well
|
||
|
|
|
||
|
|
% id = "01H9R1KJESD2KED5TAFBY426A6"
|
||
|
|
- (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.)
|
||
|
|
|
||
|
|
% id = "01H9R1KJESES27VKVW4A0ZVM11"
|
||
|
|
- we intended for `_remaining_hugs` to be private, but if hugs are enabled, it becomes public.
|
||
|
|
|
||
|
|
% id = "01H9R1KJESTKW90R788SSPMNC6"
|
||
|
|
- this can be _very_ hard to spot if you have a big class with lots of declarations inside.
|
||
|
|
|
||
|
|
% id = "01H9R1KJESCJ3VC8ATPYFDCPSP"
|
||
|
|
- this can be worked around by banning access modifiers from appearing in `#ifdef`s, but you have to *realize* that this might happen
|
||
|
|
|
||
|
|
% id = "01H9R1KJES4ZYHVADDF80WAXH6"
|
||
|
|
- 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()` specifiers)
|
||
|
|
|
||
|
|
% id = "01H9R1KJES182MCV2V0A4VHKKX"
|
||
|
|
- even if we didn't have the preprocessor, that access modifier is state _you_ have to keep track of
|
||
|
|
|
||
|
|
% id = "01H9R1KJESH7PWNKCKW3H0WJHW"
|
||
|
|
- 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
|
||
|
|
|
||
|
|
% id = "01H9R1KJESFE6F1D4J5PA5Q381"
|
||
|
|
- (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)
|