Description

Helper functions for contiguous enums.

Contiguous Enums
Enum Ranges
Array indexed with an enum
Cast to enums
String conversion

Contiguous Enums

Contiguous enums are enums whose enumerator values form a range of 0 to max, which means there is no gap in between the values. For example, if no enumerator values are specified, an enum is contiguous as in the following example:

enum class myenum : std::uint8_t
{
  val1,
  val2
};

Most function of this library need to know the enum's maximum value, or its number of enumerators, for that matter. Unfortunately, C++ offers no introspection of any kind which makes it possible to query the maximum value. fcppt provides a trait class called fcppt::enum_::max_value, which can be quickly specialized by using FCPPT_ENUM_DEFINE_MAX_VALUE in the global namespace, for example:

FCPPT_ENUM_DEFINE_MAX_VALUE(myenum::val2)

Building on top of this, fcppt::enum_::size calculates the number of enumerators in an enum, setting it to fcppt::enum_::max_value<Enum> + 1 by default.

Enum Ranges

Given the above definition of contiguous enums, it is possible to create a range that iterates over an enum.

  // Prints 0, 1
  for (myenum const value : fcppt::enum_::make_range<myenum>())
  {
    print_enum(value);
  }

fcppt::enum_::make_range creates an fcppt::enum_::range which uses fcppt::enum_::iterator. To create subranges of enums, there are fcppt::enum_::make_range_start and fcppt::enum_::make_range_start_end.

Array indexed with an enum

A contiguous enum is also a range of constant size, making it suitable as an index for an fcppt::array::object. fcppt::enum_::array is a class that wraps fcppt::array::object, replacing all indices by Enums, for example:

  using array = fcppt::enum_::array<myenum, bool>;
 
  array const val{true, false};
 
  std::cout << val[myenum::val1] << '\n';

Cast to enums

Casting an integral value to an enum might be needed when deserializing data. It is important, however, that the value must not fall outside of the enum's range. fcppt::enum_::from_int returns an empty optional in this case.

String conversion

Converting enums from and to strings is also often needed. Unfortunately, because C++ offers no introspection of any kind for enums, we have to provide our own mapping from enums to strings. To implement this for a custom enum type Enum, we have to specialize the struct fcppt::enum_::to_string_impl and implement a member function std::string get(Enum). For example:

namespace fcppt::enum_
{
template <>
struct to_string_impl<myenum>
{
  static std::string_view get(myenum const _value)
  {
    FCPPT_PP_PUSH_WARNING
    FCPPT_PP_DISABLE_GCC_WARNING(-Wswitch-default)
    switch (_value)
    {
    case myenum::val1:
      return "val1";
    case myenum::val2:
      return "val2";
    }
    FCPPT_PP_POP_WARNING
    throw fcppt::enum_::make_invalid(_value);
  }
};
}

We can now use fcppt::enum_::to_string to convert myenum to a string:

myenum const test{myenum::val2};

std::string const converted{fcppt::enum_::to_string(test)};

Similarly, we can also try to convert a string to an enum: fcppt::enum_::from_string uses fcppt::enum_::from_string_impl, which by default simply goes through all possible enum names. If no enum name matches, an empty optional is returned:

  // Returns an empty optional
  fcppt::optional::object<myenum> const enum1{
      fcppt::enum_::from_string<myenum>("test")};
 
  // Returns myenum::val1
  fcppt::optional::object<myenum> const enum2{
      fcppt::enum_::from_string<myenum>("val1")};

The functions fcppt::enum_::input and fcppt::enum_::output make use of fcppt::enum_::from_string and fcppt::enum_::to_string respectively. They can be used to implement operator>> and operator<<.

Classes
class	fcppt::enum_::array< Enum, Value >
	An array indexed with an enum. More...

class	fcppt::enum_::invalid< Enum >
	Exception to use for invalid enums. More...

class	fcppt::enum_::iterator< Enum >

struct	fcppt::enum_::max_value_impl< Type >
	Specialization point for max_value. More...

class	fcppt::enum_::range< Enum >
	A range over a contiguous enum. More...

struct	fcppt::enum_::to_string_impl< Enum, Enable >
	Customization point for fcppt::enum_::to_string. More...

Macros
#define	FCPPT_ENUM_DEFINE_MAX_VALUE(value)
	Specialize fcppt::enum_::max_value_impl using a macro.

#define	FCPPT_ENUM_TO_STRING_CASE(type, name)
	Generates a case for the implementation of fcppt::enum_::to_string_impl.

Typedefs
template<typename Type, typename = std::enable_if_t<fcppt::enum_::is_object<Type>::value>>
using	fcppt::enum_::max_value = typename fcppt::enum_::max_value_impl<Type>::type
	The maximum enumerator in an enum.

template<typename Type, typename = std::enable_if_t<fcppt::enum_::is_object<Type>::value>>
using	fcppt::enum_::min_value = std::integral_constant<Type, fcppt::cast::int_to_enum<Type>(0)>
	The minimum enumerator in an enum.

template<typename Enum>
using	fcppt::enum_::names_array = fcppt::enum_::array<Enum, std::string_view>
	Array type for The names of an enum.

template<typename Type>
using	fcppt::enum_::size
	The number of enumerators in an enum.

template<typename Type>
using	fcppt::enum_::size_type = typename fcppt::enum_::size_type_impl<Type>::type
	The size type used to count the number of enumerators in an enum.

template<typename Enum>
using	fcppt::mpl::list::enum_range
	An mpl::list::object over an enum.

template<fcppt::type_traits::enum_constant_concept Start, fcppt::type_traits::enum_constant_concept Max>
using	fcppt::mpl::list::enum_range_start_end
	An mpl::list::object over enums from a minimum to a maximum.

Functions
template<typename Enum, typename Value>
bool	fcppt::enum_::operator== (fcppt::enum_::array< Enum, Value > const &_a, fcppt::enum_::array< Enum, Value > const &_b)
	Compares two enum arrays for equality.

template<typename Enum, typename Value>
bool	fcppt::enum_::operator!= (fcppt::enum_::array< Enum, Value > const &_a, fcppt::enum_::array< Enum, Value > const &_b)
	Compares two enum arrays for inequality.

template<typename Array, typename Function>
Array	fcppt::enum_::array_init (Function const &_function)
	Constructs an array by calling a function with static enumerators.

template<typename Array, typename Function>
auto	fcppt::enum_::array_map (Array &&_source, Function const &_function) -> fcppt::enum_::array< typename std::remove_cvref_t< Array >::enum_type, decltype(_function(fcppt::move_if_rvalue< Array >(std::declval< fcppt::container::to_reference_type< std::remove_reference_t< Array > > >())))>
	Applies a function to every element of an enum_::array and returns an enum_::array of the results.

template<typename Ch, typename Traits, typename Enum, typename Value> requires (fcppt::enum_::is_object<Enum>::value)
std::basic_ostream< Ch, Traits > &	fcppt::enum_::operator<< (std::basic_ostream< Ch, Traits > &_stream, fcppt::enum_::array< Enum, Value > const &_array)
	Outputs an enum array.

template<typename Enum, typename Value> requires (std::is_unsigned_v<Value> && fcppt::enum_::is_object<Enum>::value)
fcppt::optional::object< Enum >	fcppt::enum_::from_int (Value const &_value) noexcept
	Cast an unsigned value to an enum.

template<typename Enum> requires (fcppt::enum_::is_object<Enum>::value)
fcppt::optional::object< Enum >	fcppt::enum_::from_string (std::string_view const _string)
	Converts a string to an enum.

template<typename Enum, typename Value>
fcppt::optional::object< Enum >	fcppt::enum_::index_of_array (fcppt::enum_::array< Enum, Value > const &_array, Value const &_value)
	Returns the enum of the first element found in an enum array.

template<typename Ch, typename Traits, typename Enum> requires (fcppt::enum_::is_object<Enum>::value)
std::basic_istream< Ch, Traits > &	fcppt::enum_::input (std::basic_istream< Ch, Traits > &_stream, Enum &_result)
	Reads an enum value from a stream.

template<typename Enum>
fcppt::enum_::invalid< Enum >	fcppt::enum_::make_invalid (Enum const _enum)

template<typename Enum>
fcppt::enum_::range< Enum >	fcppt::enum_::make_range () noexcept
	Creates an enum range over the whole enum.

template<typename Enum>
fcppt::enum_::range< Enum >	fcppt::enum_::make_range_start (Enum const _start) noexcept
	Creates an enum range with a custom start value.

template<typename Enum>
fcppt::enum_::range< Enum >	fcppt::enum_::make_range_start_end (Enum const _start, Enum const _end) noexcept
	Creates a closed enum range.

template<typename Enum> requires (fcppt::enum_::is_object<Enum>::value)
fcppt::enum_::names_array< Enum >	fcppt::enum_::names ()
	The names of an enum type.

template<typename Ch, typename Traits, typename Enum> requires (fcppt::enum_::is_object<Enum>::value)
std::basic_ostream< Ch, Traits > &	fcppt::enum_::output (std::basic_ostream< Ch, Traits > &_stream, Enum const _value)
	Outputs an enum value to a stream.

template<typename Enum, typename Function> requires (fcppt::enum_::is_object<Enum>::value)
decltype(auto)	fcppt::enum_::to_static (Enum const _enum, Function const &_function)
	Converts a runtime enum value into a compile time one, passing it to a function.

template<typename Enum> requires (fcppt::enum_::is_object<Enum>::value)
std::string_view	fcppt::enum_::to_string (Enum const _enum)
	Converts an enum to a string.

Macro Definition Documentation

◆ FCPPT_ENUM_DEFINE_MAX_VALUE

#define FCPPT_ENUM_DEFINE_MAX_VALUE ( value )

Value:

namespace fcppt::enum_ { \
template<> struct max_value_impl<decltype(value)> { \
  using type = std::integral_constant<decltype(value), value>; \
};\
}

Specialize fcppt::enum_::max_value_impl using a macro.

◆ FCPPT_ENUM_TO_STRING_CASE

#define FCPPT_ENUM_TO_STRING_CASE	(		type,
			name )

Value:

case type::name: return #name

Generates a case for the implementation of fcppt::enum_::to_string_impl.

Typedef Documentation

◆ enum_range

template<typename Enum>

using fcppt::mpl::list::enum_range

Initial value:

fcppt::mpl::list::

enum_range_start_end<fcppt::enum_::min_value<Enum>, fcppt::enum_::max_value<Enum>>

An mpl::list::object over an enum.

The result is

mpl::list::object<fcppt::enum_::min_value<Enum>, ..., fcppt::enum_::max_value<Enum>>

TODO(concepts)

◆ enum_range_start_end

template<fcppt::type_traits::enum_constant_concept Start, fcppt::type_traits::enum_constant_concept Max>

using fcppt::mpl::list::enum_range_start_end

Initial value:

typename fcppt::mpl::list::detail::enum_range_start_end<Start, Max>::type

An mpl::list::object over enums from a minimum to a maximum.

Let Start = std::integral_constant<Enum,S> and Max = std::integral_constant<Enum,M>. Then the result is

mpl::list::object<std::integral_constant<Enum,S>, std::integral_constant<Enum,S + 1>, ..., std::integral_constant<Enum,M>>

◆ max_value

template<typename Type, typename = std::enable_if_t<fcppt::enum_::is_object<Type>::value>>

using fcppt::enum_::max_value = typename fcppt::enum_::max_value_impl<Type>::type

The maximum enumerator in an enum.

This class defines the maximum enumerator (the enumerator with the biggest integral value) in the enum denoted by Type. The default behaviour is to use Type::fcppt_maximum. Specialize fcppt::enum_::max_value_impl to change that.

Note: Unfortunately, there is no way to automatically retrieve the maximum enumerator in an enum in C++.

Template Parameters

Type	Must be an enum type.

◆ min_value

template<typename Type, typename = std::enable_if_t<fcppt::enum_::is_object<Type>::value>>

using fcppt::enum_::min_value = std::integral_constant<Type, fcppt::cast::int_to_enum<Type>(0)>

The minimum enumerator in an enum.

Template Parameters

Type	Must be an enum type

◆ names_array

template<typename Enum>

using fcppt::enum_::names_array = fcppt::enum_::array<Enum, std::string_view>

Array type for The names of an enum.

Template Parameters

Enum	Must be an enum type.

◆ size

template<typename Type>

using fcppt::enum_::size

Initial value:

std::integral_constant<

fcppt::enum_::size_type<Type>,

fcppt::cast::enum_to_int<fcppt::enum_::size_type<Type>>(fcppt::enum_::max_value<Type>::value) +

1U>

The number of enumerators in an enum.

This class defines the number of enumerators in the enum denoted by Type. The default behavior is to set it to use fcppt::enum_::max_value<Type> + 1. Specialize this class to change that.

Note: Unfortunately, there is no way to automatically retrieve the number of enumerators in an enum in C++.

Template Parameters

Type	Must be an enum type

◆ size_type

template<typename Type>

using fcppt::enum_::size_type = typename fcppt::enum_::size_type_impl<Type>::type

The size type used to count the number of enumerators in an enum.

The size type used to count the number of enumerators in Type.

Template Parameters

Type	Must be an enum type

Function Documentation

◆ array_init()

template<typename Array, typename Function>

Array fcppt::enum_::array_init ( Function const & _function )

inline

Constructs an array by calling a function with static enumerators.

Constructs an enum array of type Array by calling _function(std::integral_constant<Array::enum_type,E>) for every enumerator E.

Template Parameters

Array	Must be an fcppt::enum_::array.
Function	Must be a function callable as `Array::value_type (std::integral_constant<Array::enum_type,E>)`.

See also: fcppt::array::init

◆ array_map()

template<typename Array, typename Function>

auto fcppt::enum_::array_map	(	Array &&	_source,
		Function const &	_function ) -> fcppt::enum_::array< typename std::remove_cvref_t<Array>::enum_type, decltype(_function(fcppt::move_if_rvalue<Array>( std::declval<fcppt::container::to_reference_type<std::remove_reference_t<Array>>>())))>

inline

Applies a function to every element of an enum_::array and returns an enum_::array of the results.

◆ from_int()

template<typename Enum, typename Value>
requires (std::is_unsigned_v<Value> && fcppt::enum_::is_object<Enum>::value)

fcppt::optional::object< Enum > fcppt::enum_::from_int ( Value const & _value )

noexcept

Cast an unsigned value to an enum.

Casts the unsigned value _value to Enum. Returns an empty optional if the cast fails.

Parameters

_value The value to cast from

Template Parameters

Enum	Must be an enum type
Value	Must be an unsigned type

◆ from_string()

template<typename Enum>
requires (fcppt::enum_::is_object<Enum>::value)

fcppt::optional::object< Enum > fcppt::enum_::from_string ( std::string_view const _string )

inline

Converts a string to an enum.

Uses fcppt::enum_::from_string_impl to convert a string to an enum.

Template Parameters

Enum	Must be an enum type

◆ index_of_array()

template<typename Enum, typename Value>

fcppt::optional::object< Enum > fcppt::enum_::index_of_array	(	fcppt::enum_::array< Enum, Value > const &	_array,
		Value const &	_value )

inline

Returns the enum of the first element found in an enum array.

Searches for _value in _array and returns the index of the first occurrence as an enum if there is any, otherwise returns the empty optional.

◆ input()

template<typename Ch, typename Traits, typename Enum>
requires (fcppt::enum_::is_object<Enum>::value)

std::basic_istream< Ch, Traits > & fcppt::enum_::input	(	std::basic_istream< Ch, Traits > &	_stream,
		Enum &	_result )

Reads an enum value from a stream.

Uses fcppt::enum_::from_string to read an enum from _stream and store it in _result. In case this fails, the failbit of _stream is set. This function is useful to implement operator>> for an enum type.

Template Parameters

Enum	Must be an enum type

Returns: _stream

◆ make_invalid()

template<typename Enum>

fcppt::enum_::invalid< Enum > fcppt::enum_::make_invalid ( Enum const _enum )

inlinenodiscard

◆ make_range()

template<typename Enum>

fcppt::enum_::range< Enum > fcppt::enum_::make_range ( )

inlinenoexcept

Creates an enum range over the whole enum.

Creates the enum range [fcppt::enum_::min_value<Enum>::value, fcppt::enum_::max_value<Enum>::value].

◆ make_range_start()

template<typename Enum>

fcppt::enum_::range< Enum > fcppt::enum_::make_range_start ( Enum const _start )

inlinenoexcept

Creates an enum range with a custom start value.

Creates the closed range [_start, enum_max_value<Enum>::value].

Parameters

_start The first element of the range.

◆ make_range_start_end()

template<typename Enum>

fcppt::enum_::range< Enum > fcppt::enum_::make_range_start_end	(	Enum const	_start,
		Enum const	_end )

inlinenoexcept

Creates a closed enum range.

Creates the enum range [_start,_end]. The range must be closed because there is no "one past the end" enum value.

Parameters

_start	The first element of the range.
_end	The last element of the range.

◆ names()

template<typename Enum>
requires (fcppt::enum_::is_object<Enum>::value)

fcppt::enum_::names_array< Enum > fcppt::enum_::names ( )

inline

The names of an enum type.

Template Parameters

Enum	Must be an enum type

◆ operator!=()

template<typename Enum, typename Value>

bool fcppt::enum_::operator!=	(	fcppt::enum_::array< Enum, Value > const &	_a,
		fcppt::enum_::array< Enum, Value > const &	_b )

inline

Compares two enum arrays for inequality.

Template Parameters

Value Must be equality-comparable.

◆ operator<<()

template<typename Ch, typename Traits, typename Enum, typename Value>
requires (fcppt::enum_::is_object<Enum>::value)

std::basic_ostream< Ch, Traits > & fcppt::enum_::operator<<	(	std::basic_ostream< Ch, Traits > &	_stream,
		fcppt::enum_::array< Enum, Value > const &	_array )

Outputs an enum array.

◆ operator==()

template<typename Enum, typename Value>

bool fcppt::enum_::operator==	(	fcppt::enum_::array< Enum, Value > const &	_a,
		fcppt::enum_::array< Enum, Value > const &	_b )

Compares two enum arrays for equality.

Template Parameters

Value Must be equality-comparable.

◆ output()

template<typename Ch, typename Traits, typename Enum>
requires (fcppt::enum_::is_object<Enum>::value)

std::basic_ostream< Ch, Traits > & fcppt::enum_::output	(	std::basic_ostream< Ch, Traits > &	_stream,
		Enum const	_value )

Outputs an enum value to a stream.

Uses fcppt::enum_::to_string to output _value to _stream. This function is useful to implement operator<< for an enum type.

Template Parameters

Enum	Must be an enum type

Returns: _stream

◆ to_static()

template<typename Enum, typename Function>
requires (fcppt::enum_::is_object<Enum>::value)

decltype(auto) fcppt::enum_::to_static	(	Enum const	_enum,
		Function const &	_function )

inline

Converts a runtime enum value into a compile time one, passing it to a function.

Template Parameters

Function A function callable as R (std::integal_constant<Enum,E>), where R is the result type.

◆ to_string()

template<typename Enum>
requires (fcppt::enum_::is_object<Enum>::value)

std::string_view fcppt::enum_::to_string ( Enum const _enum )

inline

Converts an enum to a string.

Uses fcppt::enum_::to_string_impl to convert an enum to a string.

Template Parameters

Enum	Must be an enum type

Description

Contiguous Enums

Enum Ranges

Array indexed with an enum

Cast to enums

String conversion

Classes

Macros

Typedefs

Functions

Macro Definition Documentation

◆ FCPPT_ENUM_DEFINE_MAX_VALUE

◆ FCPPT_ENUM_TO_STRING_CASE

Typedef Documentation

◆ enum_range

◆ enum_range_start_end

◆ max_value

◆ min_value

◆ names_array

◆ size

◆ size_type

Function Documentation

◆ array_init()

◆ array_map()

◆ from_int()

◆ from_string()

◆ index_of_array()

◆ input()

◆ make_invalid()

◆ make_range()

◆ make_range_start()

◆ make_range_start_end()

◆ names()

◆ operator!=()

◆ operator<<()

◆ operator==()

◆ output()

◆ to_static()

◆ to_string()