James Ward | 22a4e15 | 2020-09-25 11:43:21 +0100 | [diff] [blame] | 1 | #ifndef VARIANT_CAST_HPP |
| 2 | #define VARIANT_CAST_HPP |
| 3 | |
| 4 | #include <type_traits> |
| 5 | |
| 6 | namespace mapbox { |
| 7 | namespace util { |
| 8 | |
| 9 | namespace detail { |
| 10 | |
| 11 | template <class T> |
| 12 | class static_caster |
| 13 | { |
| 14 | public: |
| 15 | template <class V> |
| 16 | T& operator()(V& v) const |
| 17 | { |
| 18 | return static_cast<T&>(v); |
| 19 | } |
| 20 | }; |
| 21 | |
| 22 | template <class T> |
| 23 | class dynamic_caster |
| 24 | { |
| 25 | public: |
| 26 | using result_type = T&; |
| 27 | template <class V> |
| 28 | T& operator()(V& v, typename std::enable_if<!std::is_polymorphic<V>::value>::type* = nullptr) const |
| 29 | { |
| 30 | throw std::bad_cast(); |
| 31 | } |
| 32 | template <class V> |
| 33 | T& operator()(V& v, typename std::enable_if<std::is_polymorphic<V>::value>::type* = nullptr) const |
| 34 | { |
| 35 | return dynamic_cast<T&>(v); |
| 36 | } |
| 37 | }; |
| 38 | |
| 39 | template <class T> |
| 40 | class dynamic_caster<T*> |
| 41 | { |
| 42 | public: |
| 43 | using result_type = T*; |
| 44 | template <class V> |
| 45 | T* operator()(V& v, typename std::enable_if<!std::is_polymorphic<V>::value>::type* = nullptr) const |
| 46 | { |
| 47 | return nullptr; |
| 48 | } |
| 49 | template <class V> |
| 50 | T* operator()(V& v, typename std::enable_if<std::is_polymorphic<V>::value>::type* = nullptr) const |
| 51 | { |
| 52 | return dynamic_cast<T*>(&v); |
| 53 | } |
| 54 | }; |
| 55 | } |
| 56 | |
| 57 | template <class T, class V> |
| 58 | typename detail::dynamic_caster<T>::result_type |
| 59 | dynamic_variant_cast(V& v) |
| 60 | { |
| 61 | return mapbox::util::apply_visitor(detail::dynamic_caster<T>(), v); |
| 62 | } |
| 63 | |
| 64 | template <class T, class V> |
| 65 | typename detail::dynamic_caster<const T>::result_type |
| 66 | dynamic_variant_cast(const V& v) |
| 67 | { |
| 68 | return mapbox::util::apply_visitor(detail::dynamic_caster<const T>(), v); |
| 69 | } |
| 70 | |
| 71 | template <class T, class V> |
| 72 | T& static_variant_cast(V& v) |
| 73 | { |
| 74 | return mapbox::util::apply_visitor(detail::static_caster<T>(), v); |
| 75 | } |
| 76 | |
| 77 | template <class T, class V> |
| 78 | const T& static_variant_cast(const V& v) |
| 79 | { |
| 80 | return mapbox::util::apply_visitor(detail::static_caster<const T>(), v); |
| 81 | } |
| 82 | } |
| 83 | } |
| 84 | |
| 85 | #endif // VARIANT_CAST_HPP |