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> If you leave out the this pointer, it is the equivalent of putting a function pointer to a global function (or a static member function) into the structure.

No it is not. Unless you can show me a virtual overridden static member function.

> since hypothetical child classes would not be able to override the definition while using the this pointer

Yes! That's the entire idea here. The non-hypothetical, but indeed existing, child classes are not able to access the object. This is to prescribe potential behaviour for child implementations.