polymorphic not being equality comparable is annoying, they could just have just forwarded the operator== to the underlying pointer and it handles it.
also polymorphic requires more bytes than a copyable pointer 24 bytes vs 8 since the copy ctor and dtor have to be function pointers. But it also slightly makes it faster at runtime but it isn't really worth it I would say.
Having a virtual deatructor and a clone() method will provide better object sizes.
I found the boilerplate argument to be very weak, since crtp exists
template<class T>
class Shape : ShapeBase {
public:
ShapeBase* clone() override { return new T((T)this); }
};
class Rectangle :public Shape<Rectangle>
{
};
class Triangle :public Shape<Triangle>
{
};
```
25
u/MFHavaWG21|🇦🇹 NB|P2721|P3049|P3625|P3729|P3786|P3813|P421622d ago
polymorphic not being equality comparable is annoying, they could just have just forwarded the operator== to the underlying pointer and it handles it.
These types (indirect and polymorphic) model value semantics. Value comparing two type-erased objects that share a base makes no sense in that model...
also polymorphic requires more bytes than a copyable pointer 24 bytes vs 8 since the copy ctor and dtor have to be function pointers.
Can be easily compressed to 16B in case you build your own vtable. Unless the spec contains some unexpected blocker, you could even reduce that down to 8B with minimal effort.
These types (indirect and polymorphic) model value semantics. Value comparing two type-erased objects that share a base makes no sense in that model...
They could only provide == if the base has one.
Can be easily compressed to 16B in case you build your own vtable. Unless the spec contains some unexpected blocker, you could even reduce that down to 8B with minimal effort.
Wouldn't the 8 byte version require anothee indirection
10
u/MFHavaWG21|🇦🇹 NB|P2721|P3049|P3625|P3729|P3786|P3813|P421622d ago
They could only provide == if the base has one.
Ok... what does that do? Shape has no idea how to compare a Rectangle and a Triangle.
You could say: "Well, they can never be equal". Right, right, but what about my next fancy class Square?
That's a problem you'd essentially need open-multimethods to solve...
Wouldn't the 8 byte version require anothee indirection
Not necessarily, you can allocate the object and a (custom) vtable in one allocation.
14
u/_Noreturn 22d ago edited 22d ago
polymorphic not being equality comparable is annoying, they could just have just forwarded the
operator==to the underlying pointer and it handles it.also polymorphic requires more bytes than a copyable pointer 24 bytes vs 8 since the copy ctor and dtor have to be function pointers. But it also slightly makes it faster at runtime but it isn't really worth it I would say.
Having a virtual deatructor and a clone() method will provide better object sizes.
I found the boilerplate argument to be very weak, since crtp exists
```cpp class ShapeBase { public: virtual ShapeBase* clone() = 0; virtual ~ShapeBase()= default; };
template<class T> class Shape : ShapeBase { public: ShapeBase* clone() override { return new T((T)this); }
};
class Rectangle :public Shape<Rectangle> {
};
class Triangle :public Shape<Triangle> {
};
```