Provides a more convenient way to work with different kinds of dynamically polymorphic values

asis.hpp

#ifndef UT_ASIS
#define UT_ASIS
#include <memory>
#include <type_traits>

namespace ut {

/**
 * Try to downcast from reference type `From` to pointer to `To`.
 *
 * If cast cannot be performed, returns `nullptr`.
 *
 * Preserves constness.
 */
template<typename To, typename From>
auto as(From &&f) requires(
    std::has_virtual_destructor_v<std::remove_reference_t<From>> &&std::is_base_of_v<std::remove_reference_t<From>, To>) {
    using Ret = std::conditional_t<std::is_const_v<std::remove_reference_t<From>>, To const *, To *>;
    return dynamic_cast<Ret>(&f);
}

/**
 * Try to downcast from pointer type `From` to pointer to `To`.
 *
 * If cast cannot be performed, returns `nullptr`.
 *
 * Preserves constness.
 */
template<typename To, typename From>
auto as(From *f) requires(std::has_virtual_destructor_v<From> &&std::is_base_of_v<From, To>

) {
    using Ret = std::conditional_t<std::is_const_v<From>, To const *, To *>;
    return dynamic_cast<Ret>(f);
}

/**
 * Try to downcast from `unique_ptr<From>` to pointer to `To`.
 *
 * If cast cannot be performed, returns `nullptr`.
 *
 * Preserves constness.
 */
template<typename To, typename From>
auto as(std::unique_ptr<From> const &f) requires(std::has_virtual_destructor_v<From> &&std::is_base_of_v<From, To>) {
    using Ret = std::conditional_t<std::is_const_v<From>, To const *, To *>;
    return dynamic_cast<Ret>(f.get());
}

/**
 * Try to downcast from `shared_ptr<From>` to pointer to `To`.
 *
 * If cast cannot be performed, returns `nullptr`.
 *
 * Preserves constness.
 */
template<typename To, typename From>
auto as(std::shared_ptr<From> const &f) requires(std::has_virtual_destructor_v<From> &&std::is_base_of_v<From, To>) {
    using Ret = std::conditional_t<std::is_const_v<From>, To const *, To *>;
    return dynamic_cast<Ret>(f.get());
}

/**
 * Checks if `From` has dynamic type `To`
 */
template<typename To, typename From>
bool is(From &&f) {
    return !!as<To>(std::forward<From>(f));
}

}  // namespace ut

#endif  // UT_ASIS

zzz_description

Provides a more convenient way to work with different kinds of dynamically polymorphic values.