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https://github.com/aantron/better-enums.git
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Added non-throwing versions of enum introduction functions.
These return values of an optional type better_enums::optional<T>. This type is defined in the spirit of boost::optional<T> and std::optional<T>, but is easy to manipulate at compile time. Two additional macros BETTER_ENUMS_USE_OPTIONAL and BETTER_ENUMS_EXTRA_INCLUDE are honored, whose intent is for the user to be able to inject an alternative option type. However, there are currently no viable alternatives. boost::optional<T> does not play well with constexpr, and I failed to make the code compile with std::optional<T>. I did not try very hard. I intend to support std::optional<T> in the future. Perhaps it will be the default, when available.
This commit is contained in:
Anton Bachin
parent
d9bd109172
commit
08dbe47edd
175
enum.h
175
enum.h
@ -10,14 +10,16 @@
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#include <cstddef> // For size_t.
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#include <stdexcept>
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#include <type_traits>
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#ifdef BETTER_ENUMS_EXTRA_INCLUDE
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# include BETTER_ENUMS_EXTRA_INCLUDE
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#endif
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#ifdef BETTER_ENUMS_MACRO_FILE
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#include BETTER_ENUMS_MACRO_FILE
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# include BETTER_ENUMS_MACRO_FILE
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#else
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#define _ENUM_PP_MAP(macro, data, ...) \
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@ -335,10 +337,78 @@
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namespace better_enums {
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#ifdef BETTER_ENUMS_USE_OPTIONAL
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template <typename T>
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using optional = BETTER_ENUMS_USE_OPTIONAL<T>;
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#else
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template <typename T>
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constexpr T _default()
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{
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return (typename T::_Enumerated)0;
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}
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template <>
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constexpr const char* _default<const char*>()
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{
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return nullptr;
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}
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template <>
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constexpr size_t _default<size_t>()
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{
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return 0;
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}
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template <typename T>
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struct optional {
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constexpr optional() : _valid(false), _value(_default<T>()) { }
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constexpr optional(T value) : _valid(true), _value(value) { }
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constexpr const T& operator *() const { return _value; }
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constexpr const T& operator ->() const { return _value; }
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constexpr operator bool() const { return _valid; }
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constexpr const T& value() const { return _value; }
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private:
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bool _valid;
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T _value;
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};
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#endif
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}
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namespace _enum {
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template <typename T>
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using _optional = better_enums::optional<T>;
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template <typename CastTo, typename Element>
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constexpr static _optional<CastTo>
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_map_index(const Element *array, _optional<size_t> index)
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{
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return index ? (CastTo)array[*index] : _optional<CastTo>();
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}
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template <typename T>
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constexpr static T _or_throw(_optional<T> maybe, const char *message)
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{
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return maybe ? *maybe : throw std::runtime_error(message);
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}
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template <typename Element>
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struct _Iterable {
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using iterator = const Element*;
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@ -547,7 +617,6 @@ constexpr const _Iterable<const char*> _names{_name_array, _size}; \
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}
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#define _ENUM_NS(EnumType) _enum::_data_ ## EnumType
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#define _ENUM_NOT_FOUND ((size_t)-1)
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#ifndef BETTER_ENUMS_SAFER_SWITCH
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@ -568,6 +637,9 @@ class EnumType : public _ENUM_NS(EnumType)::_Base { \
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constexpr static auto _value_array = _ENUM_NS(EnumType)::_value_array; \
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constexpr static auto _name_array = _ENUM_NS(EnumType)::_name_array; \
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\
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template <typename T> \
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using _optional = better_enums::optional<T>; \
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\
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public: \
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using _Integral = Integral; \
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\
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@ -583,9 +655,18 @@ class EnumType : public _ENUM_NS(EnumType)::_Base { \
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return _value; \
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} \
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\
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constexpr static const _optional<EnumType> \
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_from_integral_nothrow(_Integral value) \
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{ \
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return \
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_enum::_map_index<EnumType>(_value_array, _from_int_loop(value)); \
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} \
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\
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constexpr static const EnumType _from_integral(_Integral value) \
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{ \
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return _value_array[_from_int_loop(value, true)]; \
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return \
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_enum::_or_throw(_from_integral_nothrow(value), \
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"_from_integral_or_throw: invalid argument"); \
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} \
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\
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constexpr static const EnumType _from_integral_unchecked(_Integral value) \
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@ -595,32 +676,55 @@ class EnumType : public _ENUM_NS(EnumType)::_Base { \
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\
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constexpr const char* to_string() const \
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{ \
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return _name_array[_from_int_loop(_value, true)]; \
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return \
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_enum::_or_throw( \
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_enum::_map_index<const char*>(_name_array, \
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_from_int_loop(_value)), \
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"to_string: invalid enum value"); \
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} \
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\
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constexpr static const _optional<EnumType> \
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_from_string_nothrow(const char *name) \
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{ \
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return \
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_enum::_map_index<EnumType>(_value_array, _from_string_loop(name));\
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} \
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\
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constexpr static const EnumType _from_string(const char *name) \
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{ \
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return _value_array[_from_string_loop(name, true)]; \
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return \
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_enum::_or_throw(_from_string_nothrow(name), \
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"_from_string_or_throw: invalid argument"); \
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} \
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\
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constexpr static const _optional<EnumType> \
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_from_string_nocase_nothrow(const char *name) \
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{ \
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return \
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_enum::_map_index<EnumType>(_value_array, \
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_from_string_nocase_loop(name)); \
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} \
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\
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constexpr static const EnumType _from_string_nocase(const char *name) \
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{ \
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return _value_array[_from_string_nocase_loop(name, true)]; \
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return \
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_enum::_or_throw(_from_string_nocase_nothrow(name), \
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"_from_string_nocase_or_throw: invalid argument");\
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} \
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\
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constexpr static bool _is_valid(_Integral value) \
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{ \
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return _from_int_loop(value, false) != _ENUM_NOT_FOUND; \
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return _from_int_loop(value); \
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} \
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\
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constexpr static bool _is_valid(const char *name) \
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{ \
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return _from_string_loop(name, false) != _ENUM_NOT_FOUND; \
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return _from_string_loop(name); \
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} \
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\
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constexpr static bool _is_valid_nocase(const char *name) \
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{ \
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return _from_string_nocase_loop(name, false) != _ENUM_NOT_FOUND; \
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return _from_string_nocase_loop(name); \
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} \
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\
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_ENUM_CONVERSION_FOR_SWITCH(Integral, __VA_ARGS__); \
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@ -629,46 +733,33 @@ class EnumType : public _ENUM_NS(EnumType)::_Base { \
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constexpr static auto &_names = _ENUM_NS(EnumType)::_names; \
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\
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protected: \
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constexpr static size_t _from_int_loop(_Integral value, \
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bool throw_exception, \
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size_t index = 0) \
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constexpr static _optional<size_t> _from_int_loop(_Integral value, \
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size_t index = 0) \
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{ \
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return \
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index == _size ? \
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(throw_exception ? \
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throw std::runtime_error( \
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"Enum::_from_integral: invalid integer value") : \
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_ENUM_NOT_FOUND) : \
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_value_array[index]._value == value ? index : \
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_from_int_loop(value, throw_exception, index + 1); \
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index == _size ? _optional<size_t>() : \
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_value_array[index]._value == value ? _optional<size_t>(index) : \
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_from_int_loop(value, index + 1); \
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} \
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\
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constexpr static size_t _from_string_loop(const char *name, \
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bool throw_exception, \
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size_t index = 0) \
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constexpr static _optional<size_t> _from_string_loop(const char *name, \
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size_t index = 0) \
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{ \
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return \
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index == _size ? \
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(throw_exception ? \
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throw std::runtime_error( \
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"Enum::_from_string: invalid string argument") : \
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_ENUM_NOT_FOUND) : \
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_enum::_namesMatch(_name_array[index], name) ? index : \
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_from_string_loop(name, throw_exception, index + 1); \
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index == _size ? _optional<size_t>() : \
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_enum::_namesMatch(_name_array[index], name) ? \
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_optional<size_t>(index) : \
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_from_string_loop(name, index + 1); \
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} \
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\
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constexpr static size_t _from_string_nocase_loop(const char *name, \
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bool throw_exception, \
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size_t index = 0) \
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constexpr static _optional<size_t> \
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_from_string_nocase_loop(const char *name, size_t index = 0) \
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{ \
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return \
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index == _size ? \
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(throw_exception ? \
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throw std::runtime_error( \
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"Enum::_from_string_nocase: invalid string argument") :\
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_ENUM_NOT_FOUND) : \
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_enum::_namesMatchNocase(_name_array[index], name) ? index : \
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_from_string_nocase_loop(name, throw_exception, index + 1); \
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index == _size ? _optional<size_t>() : \
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_enum::_namesMatchNocase(_name_array[index], name) ? \
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_optional<size_t>(index) : \
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_from_string_nocase_loop(name, index + 1); \
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} \
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};
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@ -63,6 +63,18 @@ int main()
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// Conversions with the nothrow (optional) interface.
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auto maybe_channel = Channel::_from_string_nothrow("foo");
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if (maybe_channel)
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throw std::logic_error("expected conversion failure");
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maybe_channel = Channel::_from_string_nothrow("Blue");
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if (!maybe_channel)
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throw std::logic_error("expected successful conversion");
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print_channel(*maybe_channel);
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// Unsafe unchecked cast.
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channel = Channel::_from_integral_unchecked(2);
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