Standalone port of efl::Poly (yw nikki).
Moving a Poly instance erases the original.
template <typename Base, typename...Derived>
struct Poly : /* Implementation */ {
constexpr Poly() = default;
Poly(const Poly& p);
Poly(Poly&& p) noexcept;
template </* copyable */ U>
Poly(const U& u);
template </* movable */ U>
Poly(U&& u) noexcept;
Poly& operator=(const Poly& p);
Poly& operator=(Poly&& p) noexcept;
template </* copyable */ U>
Poly& operator=(const U& u);
template </* movable */ U>
Poly& operator=(U&& u) noexcept;
//=== Mutators ===//
void visit(auto&& F);
void visit(auto&& F) const;
constexpr Base* operator->();
constexpr const Base* operator->() const;
void erase() noexcept;
//=== Observers ===//
template <typename T>
constexpr bool holdsType() const noexcept;
constexpr bool holdsAny() const noexcept;
constexpr bool isEmpty() const noexcept;
};