Python Learning

[Christian Gollwitzer]

Am 18.12.17 um 05:54 schrieb Bill:
> Chris Angelico wrote:
>> I don't know about vtables as needing to be in ANY programming course.
>> They're part of a "let's dive into the internals of C++" course. You
>> certainly don't need them to understand how things work in Python,
>> because they don't exist; and I'm doubtful that you need to explain
>> them even to C++ programmers.
>>
> Then how are you going to explain dynamic_cast?
> 

You don't need to explain a vtable to explain dynamic_cast. Only if you 
want to become a compiler writer. It is not even required, vtables are 
just the most common implementation.

dynamic_cast simply checks if the actual object that the pointer points 
to is an instance of a derived class, and then casts it into that. You 
could "explain" it with the following pseudo-code

template <T*, base*>
T* dynamic_cast<T*>(base *input) {
	if (isinstanceof(base, *input)) { return (T*)input; }
	else { return nullptr; }
}

How that works (particularly the "isinstanceof") is not the business of 
the programmer - it is sufficient to know that the compiler somewhere 
stores this information for every object.

	Christian