On Thu, 11 Apr 2024 at 21:54, Tiago Freire via Std-Proposals
<std-proposals_at_[hidden]> wrote:
> For that I could design a templated class, let’s call it “doppelganger”, that can contain an object of a “derived” class but only presents itself as an interface to a “base” class.
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> i.e.
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> class A{};
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> class B: public A {};
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> std::doppelganger<A> tracked_object = B{};
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> // tracked_object can be used as A, but is an object of type B //this is a pure liskov abstraction
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> Kind of like what you already can do with std::unique_ptr but with value semantics instead.

In other words, the proposed std::polymorphic_value. https://wg21.link/p3019


> If you had this ^, would you really still need to use std::any?

Well, sometimes yes, if you have pieces of code that just transfer
anything at all from here to there.
They can transfer not just a polymorphic_value<Widget>, but any other
unrelated type as well.
The sending and receiving ends then know what to do with whatever
specific type is inside the std::any.