Enabled shared pointer for base and derived class, also get shared_from_this in constructor of each class?

Asked Apr 29 '21 at 20:00

Active Apr 29 '21 at 20:10

Viewed 48 times

There's two issues with this code:

Enabling shared from this on class B which is a derived class
Calling shared_from_this() in the constructor of each class.


class A : public std::enable_shared_from_this<A> {
public:
      A() {
          shared_from_this();
      }
};

class B : public A, public std::enable_shared_from_this<B> {
public:
      B() {
          shared_from_this();
      }
};

Is there to allow both classes to use shared_from_this from their constructors?

edited Apr 29 '21 at 20:10

463035818_is_not_an_ai

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asked Apr 29 '21 at 20:00

Tom

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what do you expect from calling `shared_from_this()` while ignoring the retuned value ? – 463035818_is_not_an_ai Apr 29 '21 at 20:03
@largest_prime_is_463035818 It's just an example of using shared_from_this() in the constructor – Tom Apr 29 '21 at 20:04
is your question how to fix this compiler error: https://godbolt.org/z/qhrfKbnob ? – 463035818_is_not_an_ai Apr 29 '21 at 20:06
2

you can´t use `shared_from_this` in a constructor even without inheritance – Alan Birtles Apr 29 '21 at 20:06
@Tom, is this an exercise? `shared_from_this` has some very specific uses and the usage in the snippet doesn't really make much sense. – Zoso Apr 29 '21 at 20:06
2

Please see ["Why shared_from_this can't be used in constructor from technical standpoint?"](https://stackoverflow.com/questions/31924396/why-shared-from-this-cant-be-used-in-constructor-from-technical-standpoint). – G.M. Apr 29 '21 at 20:06
@Zoso No, I generally want to know if this is possible – Tom Apr 29 '21 at 20:07
@largest_prime_is_463035818 Yes – Tom Apr 29 '21 at 20:08
if it wasnt `shared_from_this` you would write `std::enable_shared_from_this::shared_from_this();` instead, though as the linked answer explains this is still wrong, maybe UB, I dont know – 463035818_is_not_an_ai Apr 29 '21 at 20:13
1

it was ub, since C++17 it throws: https://en.cppreference.com/w/cpp/memory/enable_shared_from_this/shared_from_this – 463035818_is_not_an_ai Apr 29 '21 at 20:15
https://godbolt.org/z/deEzxh5qe – 463035818_is_not_an_ai Apr 29 '21 at 20:21

Enabled shared pointer for base and derived class, also get shared_from_this in constructor of each class?

0 Answers0