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A comment on C++ Patterns: The Badge. Parent comment

Re:C++ Patterns: The Badge by kazinator on Wednesday June 12, 2019 @11:50AM (#20165905)
Well, that's a problem in the C++ type system, isn't it; because it (effectively) constructs a value of type Badge<Device>, even though it's not a piece of code sitting in the Device class scope.

The rule should be that if the default constructor of T is not accessible in the scope, then any cast to T * or T & requires a diagnostic. Or something like that.

If I can allocate a suitably aligned buffer of sizeof (T) zeros, and then treat that as a T, I've effectively constructed a T.

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Re:C++ Patterns: The Badge by a1369209993 on Wednesday June 12, 2019 @05:36PM (#20169585)
No, that's a good feature of the C++ type system, because it (effectively) allows the programmer to construct a value of type Badge<Device>, even if Device thinks it's okay to prevent that.

It would be better to do eg "return Device::private:get_badge()", but C++ defectively doesn't support that.

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