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Fix Enum.4 example

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Issue #716
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Bjarne Stroustrup 2017-06-12 17:07:50 -04:00
parent 5393fab88f
commit 8cc76e2c38
1 changed files with 14 additions and 4 deletions
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CppCoreGuidelines.md
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@ -8436,16 +8436,26 @@ Convenience of use and avoidance of errors.
##### Example
enum class Day { mon, tue, wed, thu, fri, sat, sun };
enum Day { mon, tue, wed, thu, fri, sat, sun };
Day operator++(Day& d)
Day& operator++(Day& d)
{
return d == Day::sun ? Day::mon : Day{++d};
return d = (d==Day::sun) ? Day::mon : static_cast<Day>(static_cast<int>(d)+1);
}
Day today = Day::sat;
Day tomorrow = ++today;
The use of a `static_cast` is not pretty, but
Day& operator++(Day& d)
{
return d = (d== Day::sun) ? Day::mon : Day{++d}; // error
}
is an infinite recursion, and writing it without a cast, using a `switch` on all cases is longwinded.
##### Enforcement
Flag repeated expressions cast back into an enumeration.