js8544 commented on issue #33628:
URL: https://github.com/apache/arrow/issues/33628#issuecomment-1428276965
> `Scalar` has a problematic `const_cast` that makes any caller of
`GetSharedPtr` a potential violator of const-correctness.
>
> ```c++
> /// \brief EXPERIMENTAL Enable obtaining shared_ptr<Scalar> from a const
> /// Scalar& context.
> std::shared_ptr<Scalar> GetSharedPtr() const {
> return const_cast<Scalar*>(this)->shared_from_this();
> }
> ```
>
> `std::enable_shared_from_this` shows how to do this properly:
>
> ```c++
> shared_ptr<_Tp>
> shared_from_this()
> { return shared_ptr<_Tp>(this->_M_weak_this); }
>
> shared_ptr<const _Tp>
> shared_from_this() const
> { return shared_ptr<const _Tp>(this->_M_weak_this); }
> ```
I think this `const_cast` is justifiable though, since the const version of
`shared_from_this` returns `shared_ptr<const Scalar> `. To fix this we would
need to write something like a `arrow::util::enable_shared_from_this` that
returns `shared_ptr<_Tp>` for const _Tp. Do you think it's worth the hassle? cc
@felipecrv @pitrou
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