typeconverter.hpp

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#pragma once
 
#include <type_traits>
 
namespace opcua {
 
/**
 * Type conversion from and to native types.
 *
 * Native types can be both `UA_*` types and wrapper classes (like `UA_Guid` and `Guid`).
 * The `TypeConverter` is mainly used within the `Variant` class to set/get non-native types.
 *
 * Template specializations can be added for conversions of arbitrary types:
 * @code
 * namespace ::opcua {
 * template <>
 * struct TypeConverter<MyGuid> {
 *     using NativeType = UA_Guid;
 *     [[nodiscard]] static MyGuid fromNative(const UA_Guid& src) { ... }
 *     [[nodiscard]] static UA_Guid toNative(const MyGuid& src) { ... }
 * };
 * }
 * @endcode
 */
template <typename T, typename Enable = void>
struct TypeConverter;
 
/* -------------------------------------- Traits and helper ------------------------------------- */
 
template <typename T, typename = void>
struct IsConvertible : std::false_type {};
 
template <typename T>
struct IsConvertible<T, std::void_t<decltype(TypeConverter<T>{})>> : std::true_type {};
 
namespace detail {
 
template <typename T, typename = std::enable_if_t<IsConvertible<T>::value>>
[[nodiscard]] constexpr T fromNative(const typename TypeConverter<T>::NativeType& src) {
    using NativeType = typename TypeConverter<T>::NativeType;
    if constexpr (std::is_invocable_r_v<T, decltype(TypeConverter<T>::fromNative), NativeType>) {
        return TypeConverter<T>::fromNative(src);
    } else {
        T dst{};
        TypeConverter<T>::fromNative(src, dst);
        return dst;
    }
}
 
template <typename T, typename = std::enable_if_t<IsConvertible<T>::value>>
[[nodiscard]] constexpr auto toNative(const T& src) -> typename TypeConverter<T>::NativeType {
    using NativeType = typename TypeConverter<T>::NativeType;
    if constexpr (std::is_invocable_r_v<NativeType, decltype(TypeConverter<T>::toNative), T>) {
        return TypeConverter<T>::toNative(src);
    } else {
        NativeType dst{};
        TypeConverter<T>::toNative(src, dst);
        return dst;
    }
}
 
}  // namespace detail
 
}  // namespace opcua