Fix mistake about final and override not affecting final classes; reword enforcement to be clearer
#2235
Conversation
…s; reword enforcement to be clearer
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Editors call: Thanks! The text already says what you want, but we see it could be clearer. The point of C.128 is that on such a virtual function, the programmer should write one of |
| @@ -7428,14 +7428,14 @@ We want to eliminate two particular classes of errors: | |||
| * **implicit virtual**: the programmer intended the function to be implicitly virtual and it is (but readers of the code can't tell); or the programmer intended the function to be implicitly virtual but it isn't (e.g., because of a subtle parameter list mismatch); or the programmer did not intend the function to be virtual but it is (because it happens to have the same signature as a virtual in the base class) | |||
| * **implicit override**: the programmer intended the function to be implicitly an overrider and it is (but readers of the code can't tell); or the programmer intended the function to be implicitly an overrider but it isn't (e.g., because of a subtle parameter list mismatch); or the programmer did not intend the function to be an overrider but it is (because it happens to have the same signature as a virtual in the base class -- note this problem arises whether or not the function is explicitly declared virtual, because the programmer might have intended to create either a new virtual function or a new non-virtual function) | |||
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| Note: On a class defined as `final`, it doesn't matter whether you put `override` or `final` on an individual virtual function. | |||
| Note: On a class defined as `final`, individual virtual functions cannot be overridden whether or not you put `final` on them. However, using `override`, or `final` without `virtual`, on a member function of a class marked `final` ensures that it overrides a base class virtual function. | |||
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Your first sentence is confusing. It reads like you're saying that virtual functions can't be overridden in the final class. But I think what you mean is that they can't be overridden again by something derived from the final class, because nothing can derive from it. It's just a confusing way to say "you can't derive from a final class"!
The second sentence is long and awkward.
| * Compare virtual function names in base and derived classes and flag uses of the same name that does not override. | ||
| * Flag overrides with neither `override` nor `final`. | ||
| * Compare virtual function names in base and derived classes and flag uses of the same name that do not have the same signatures and thus do not override. | ||
| * Flag function overrides in derived classes containing neither `override` nor `final`. |
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This change isn't an improvement. Overrides have to be in derived classes, so adding that is redundant.
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| Note: Use `final` on functions sparingly. It does not necessarily lead to optimization, and it precludes further overriding. | ||
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| ##### Enforcement | ||
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| * Compare virtual function names in base and derived classes and flag uses of the same name that does not override. | ||
| * Flag overrides with neither `override` nor `final`. | ||
| * Compare virtual function names in base and derived classes and flag uses of the same name that do not have the same signatures and thus do not override. |
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Apart from correcting "does" to "do" (which should be fixed) this added text seems redundant, but maybe it helps clarify it if somebody isn't sure about the definition of override.
Fix mistake about
finalandoverridenot affectingfinalclasses; reword enforcement to be clearer.overrideandfinalonfinalclassesfinal, it doesn't matter whether you putoverrideorfinalon an individual virtual function.That is incorrect. The semantics change if
overrideorfinalis used on an individual virtual function. Correction:final, individual virtual functions cannot be overridden whether or not you putfinalon them. However, usingoverride, orfinalwithoutvirtual, on a member function of a class markedfinalensures that it overrides a base class virtual function.Better Wording
overridenorfinal.Better wording:
overridenorfinal.