cf::expected¶

A wrapper that contains either a value or an error. More...

#include <expected.hpp>

Public Types¶

	Name
using T	value_type Value type alias.
using E	error_type Error type alias.
using unexpected< E >	unexpected_type Unexpected type alias.

Public Functions¶

	Name
constexpr	expected() Default constructor. Value-initializes T.
	expected(const expected & o) Copy constructor.
	expected(expected && o) Move constructor.
template <typenameU =T,typename =std::enable_if_t<!std::is_same_v, expected> && !std::is_same_v, std::in_place_t> && !std::is_same_v, unexpect_t> && std::is_constructible_v>> constexpr	expected(U && v) Converting constructor from value.
template <typenameG =E,typename =std::enable_if_t>> constexpr	expected(const unexpected< G > & u) Constructor from unexpected.
template <typenameG =E,typename =std::enable_if_t>> constexpr	expected(unexpected< G > && u) Constructor from unexpected rvalue.
template <typename... Args,typename =std::enable_if_t>> constexpr	expected(std::in_place_t , Args &&... args) In-place constructor for value.
template <typename... Args,typename =std::enable_if_t>> constexpr	expected(unexpect_t , Args &&... args) Constructor for in-place error construction.
	~expected() Destructor. Destroys contained value or error.
expected &	operator=(const expected & o) Copy assignment operator.
expected &	operator=(expected && o) Move assignment operator.
template <typenameU > std::enable_if_t<!std::is_same_v< std::decay_t< U >, expected > &&std::is_constructible_v< T, U > &&std::is_assignable_v< T &, U >, expected & >	operator=(U && v) Assignment from value.
template <typenameG > expected &	operator=(const unexpected< G > & u) Assignment from unexpected.
template <typenameG > expected &	operator=(unexpected< G > && u) Assignment from unexpected rvalue.
constexpr bool	has_value() const Checks if the expected contains a value.
constexpr	operator bool() const Boolean conversion operator.
constexpr T *	operator->() Pointer operator.
constexpr const T *	operator->() const Const pointer operator.
constexpr T &	operator*() Dereference operator.
constexpr const T &	operator*() const Const dereference operator.
constexpr T &&	operator*() Rvalue dereference operator.
constexpr const T &&	operator*() const Const rvalue dereference operator.
constexpr T &	value() Returns the contained value.
constexpr const T &	value() const Returns the contained value (const lvalue).
constexpr T &&	value() Returns the contained value (rvalue).
constexpr const T &&	value() const Returns the contained value (const rvalue).
constexpr E &	error() Returns the contained error.
constexpr const E &	error() const Returns the contained error (const lvalue).
constexpr E &&	error() Returns the contained error (rvalue).
constexpr const E &&	error() const Returns the contained error (const rvalue).
template <typenameU > constexpr T	value_or(U && default_val) const Returns the contained value or a default value.
template <typenameU > constexpr T	value_or(U && default_val) Returns the contained value or a default value (rvalue).
template <typenameU > constexpr E	error_or(U && default_err) const Returns the contained error or a default error.
template <typenameU > constexpr E	error_or(U && default_err) Returns the contained error or a default error (rvalue).
template <typenameF > auto	and_then(F && f) Monadic operation: chains if value is present.
template <typenameF > auto	and_then(F && f) const Monadic operation: chains if value is present (const).
template <typenameF > auto	and_then(F && f) Monadic operation: chains if value is present (rvalue).
template <typenameF > auto	or_else(F && f) Monadic operation: chains if error is present.
template <typenameF > auto	or_else(F && f) const Monadic operation: chains if error is present (const).
template <typenameF > auto	or_else(F && f) Monadic operation: chains if error is present (rvalue).
template <typenameF > auto	transform(F && f) Monadic operation: transforms the value.
template <typenameF > auto	transform(F && f) const Monadic operation: transforms the value (const).
template <typenameF > auto	transform(F && f) Monadic operation: transforms the value (rvalue).
template <typenameF > auto	transform_error(F && f) Monadic operation: transforms the error.
template <typenameF > auto	transform_error(F && f) const Monadic operation: transforms the error (const).
template <typenameF > auto	transform_error(F && f) Monadic operation: transforms the error (rvalue).
void	swap(expected & o) Swaps the contents with another expected.

Friends¶

	Name
constexpr bool	operator==(const expected & a, const expected< T2, E2 > & b) Equality comparison with another expected.
constexpr bool	operator==(const expected & a, const T2 & v) Equality comparison with a value.
constexpr bool	operator==(const expected & a, const unexpected< E2 > & u) Equality comparison with unexpected.
constexpr bool	operator!=(const expected & a, const expected< T2, E2 > & b) Inequality comparison with another expected.
constexpr bool	operator!=(const expected & a, const T2 & v) Inequality comparison with a value.
constexpr bool	operator!=(const expected & a, const unexpected< E2 > & u) Inequality comparison with unexpected.
void	swap(expected & a, expected & b) Non-member swap function.

Detailed Description¶

template <typenameT ,
typenameE >
class cf::expected;

A wrapper that contains either a value or an error.

Template Parameters:

T Value type.
E Error type.

Provides type-safe error handling without exceptions. The object either contains a value of type T or an error of type E.

Public Types Documentation¶

using value_type¶

using cf::expected< T, E >::value_type =  T;

Value type alias.

using error_type¶

using cf::expected< T, E >::error_type =  E;

Error type alias.

using unexpected_type¶

using cf::expected< T, E >::unexpected_type =  unexpected<E>;

Unexpected type alias.

Public Functions Documentation¶

function expected¶

inline constexpr expected()

Default constructor. Value-initializes T.

Exceptions:

May throw if T default constructor throws.

function expected¶

inline expected(
    constexpected & o
)

Copy constructor.

Parameters:

o Expected to copy from.

Exceptions:

May throw if T or E copy constructor throws.

function expected¶

inline expected(
    expected && o
)

Move constructor.

Parameters:

o Expected to move from.

Exceptions:

May throw if T or E move constructor throws.

function expected¶

template <typenameU  =T,
typename  =std::enable_if_t<!std::is_same_v<std::decay_t<U>, expected> &&                                          !std::is_same_v<std::decay_t<U>, std::in_place_t> &&                                          !std::is_same_v<std::decay_t<U>, unexpect_t> &&                                          std::is_constructible_v<T, U>>>
inline constexpr expected(
    U && v
)

Converting constructor from value.

Parameters:

v Value to construct with.

Exceptions:

May throw if T constructor throws.

Template Parameters:

U Forwarded value type.

function expected¶

template <typenameG  =E,
typename  =std::enable_if_t<std::is_constructible_v<E, constG&>>>
inline constexpr expected(
    constunexpected< G > & u
)

Constructor from unexpected.

Parameters:

u Unexpected value containing error.

Exceptions:

May throw if E constructor throws.

Template Parameters:

G Forwarded error type.

function expected¶

template <typenameG  =E,
typename  =std::enable_if_t<std::is_constructible_v<E, G>>>
inline constexpr expected(
    unexpected< G > && u
)

Constructor from unexpected rvalue.

Parameters:

u Unexpected value containing error.

Exceptions:

May throw if E constructor throws.

Template Parameters:

G Forwarded error type.

function expected¶

template <typename... Args,
typename  =std::enable_if_t<std::is_constructible_v<T, Args...>>>
inline explicit constexpr expected(
    std::in_place_t ,
    Args &&... args
)

In-place constructor for value.

Parameters:

args Arguments to forward to T constructor.

Exceptions:

May throw if T constructor throws.

Template Parameters:

Args Constructor argument types.

function expected¶

template <typename... Args,
typename  =std::enable_if_t<std::is_constructible_v<E, Args...>>>
inline explicit constexpr expected(
    unexpect_t ,
    Args &&... args
)

Constructor for in-place error construction.

Parameters:

args Arguments to forward to E constructor.

Exceptions:

May throw if E constructor throws.

Template Parameters:

Args Constructor argument types.

function ~expected¶

inline ~expected()

Destructor. Destroys contained value or error.

Exceptions:

None.

function operator=¶

inline expected & operator=(
    constexpected & o
)

Copy assignment operator.

Parameters:

o Expected to copy from.

Exceptions:

May throw if assignment or construction throws.

Return: Reference to this expected.

function operator=¶

inline expected & operator=(
    expected && o
)

Move assignment operator.

Parameters:

o Expected to move from.

Exceptions:

May throw if assignment or construction throws.

Return: Reference to this expected.

function operator=¶

template <typenameU >
inline std::enable_if_t<!std::is_same_v< std::decay_t< U >, expected > &&std::is_constructible_v< T, U > &&std::is_assignable_v< T &, U >, expected & > operator=(
    U && v
)

Assignment from value.

Parameters:

v Value to assign.

Exceptions:

May throw if assignment or construction throws.

Template Parameters:

U Forwarded value type.

Return: Reference to this expected.

function operator=¶

template <typenameG >
inline expected & operator=(
    constunexpected< G > & u
)

Assignment from unexpected.

Parameters:

u Unexpected value containing error.

Exceptions:

May throw if assignment or construction throws.

Template Parameters:

G Forwarded error type.

Return: Reference to this expected.

function operator=¶

template <typenameG >
inline expected & operator=(
    unexpected< G > && u
)

Assignment from unexpected rvalue.

Parameters:

u Unexpected value containing error.

Exceptions:

May throw if assignment or construction throws.

Template Parameters:

G Forwarded error type.

Return: Reference to this expected.

function has_value¶

inline constexprbool has_value() const

Checks if the expected contains a value.

Exceptions:

None.

Return: true if contains a value, false if contains error.

function operator bool¶

inline explicit constexpr operator bool() const

Boolean conversion operator.

Exceptions:

None.

Return: true if contains a value, false if contains error.

function operator->¶

inline constexprT * operator->()

Pointer operator.

Exceptions:

None.

Return: Pointer to the contained value.

Warning: Undefined behavior if expected does not contain a value.

function operator->¶

inline constexprconstT * operator->() const

Const pointer operator.

Exceptions:

None.

Return: Pointer to the contained value.

Warning: Undefined behavior if expected does not contain a value.

function operator*¶

inline constexprT & operator*()

Dereference operator.

Exceptions:

None.

Return: Reference to the contained value.

Warning: Undefined behavior if expected does not contain a value.

function operator*¶

inline constexprconstT & operator*() const

Const dereference operator.

Exceptions:

None.

Return: Const reference to the contained value.

Warning: Undefined behavior if expected does not contain a value.

function operator*¶

inline constexprT && operator*()

Rvalue dereference operator.

Exceptions:

None.

Return: Rvalue reference to the contained value.

Warning: Undefined behavior if expected does not contain a value.

function operator*¶

inline constexprconstT && operator*() const

Const rvalue dereference operator.

Exceptions:

None.

Return: Const rvalue reference to the contained value.

Warning: Undefined behavior if expected does not contain a value.

function value¶

inline constexprT & value()

Returns the contained value.

Exceptions:

bad_expected_access if expected contains an error.

Return: Reference to the contained value.

Warning: Throws bad_expected_access if this expected does not contain a value.

function value¶

inline constexprconstT & value() const

Returns the contained value (const lvalue).

Exceptions:

bad_expected_access if expected contains an error.

Return: Const reference to the contained value.

Warning: Throws bad_expected_access if this expected does not contain a value.

function value¶

inline constexprT && value()

Returns the contained value (rvalue).

Exceptions:

bad_expected_access if expected contains an error.

Return: Rvalue reference to the contained value.

Warning: Throws bad_expected_access if this expected does not contain a value.

function value¶

inline constexprconstT && value() const

Returns the contained value (const rvalue).

Exceptions:

bad_expected_access if expected contains an error.

Return: Const rvalue reference to the contained value.

Warning: Throws bad_expected_access if this expected does not contain a value.

function error¶

inline constexprE & error()

Returns the contained error.

Exceptions:

None.

Return: Reference to the contained error.

Warning: The error is only valid if has_value() returns false.

function error¶

inline constexprconstE & error() const

Returns the contained error (const lvalue).

Exceptions:

None.

Return: Const reference to the contained error.

Warning: The error is only valid if has_value() returns false.

function error¶

inline constexprE && error()

Returns the contained error (rvalue).

Exceptions:

None.

Return: Rvalue reference to the contained error.

Warning: The error is only valid if has_value() returns false.

function error¶

inline constexprconstE && error() const

Returns the contained error (const rvalue).

Exceptions:

None.

Return: Const rvalue reference to the contained error.

Warning: The error is only valid if has_value() returns false.

function value_or¶

template <typenameU >
inline constexprT value_or(
    U && default_val
) const

Returns the contained value or a default value.

Parameters:

default_val Default value to return if in error state.

Exceptions:

None.

Template Parameters:

U Default value type.

Return: The contained value or the default value.

function value_or¶

template <typenameU >
inline constexprT value_or(
    U && default_val
)

Returns the contained value or a default value (rvalue).

Parameters:

default_val Default value to return if in error state.

Exceptions:

None.

Template Parameters:

U Default value type.

Return: The contained value or the default value.

function error_or¶

template <typenameU >
inline constexprE error_or(
    U && default_err
) const

Returns the contained error or a default error.

Parameters:

default_err Default error to return if has value.

Exceptions:

None.

Template Parameters:

U Default error type.

Return: The contained error or the default error.

function error_or¶

template <typenameU >
inline constexprE error_or(
    U && default_err
)

Returns the contained error or a default error (rvalue).

Parameters:

default_err Default error to return if has value.

Exceptions:

None.

Template Parameters:

U Default error type.

Return: The contained error or the default error.

function and_then¶

template <typenameF >
inline auto and_then(
    F && f
)

Monadic operation: chains if value is present.

Parameters:

f Function to call if value is present.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: Result of f(value) or error.

function and_then¶

template <typenameF >
inline auto and_then(
    F && f
) const

Monadic operation: chains if value is present (const).

Parameters:

f Function to call if value is present.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: Result of f(value) or error.

function and_then¶

template <typenameF >
inline auto and_then(
    F && f
)

Monadic operation: chains if value is present (rvalue).

Parameters:

f Function to call if value is present.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: Result of f(value) or error.

function or_else¶

template <typenameF >
inline auto or_else(
    F && f
)

Monadic operation: chains if error is present.

Parameters:

f Function to call if error is present.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: value or result of f(error).

function or_else¶

template <typenameF >
inline auto or_else(
    F && f
) const

Monadic operation: chains if error is present (const).

Parameters:

f Function to call if error is present.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: value or result of f(error).

function or_else¶

template <typenameF >
inline auto or_else(
    F && f
)

Monadic operation: chains if error is present (rvalue).

Parameters:

f Function to call if error is present.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: value or result of f(error).

function transform¶

template <typenameF >
inline auto transform(
    F && f
)

Monadic operation: transforms the value.

Parameters:

f Function to apply to value.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: expected with transformed value or error.

function transform¶

template <typenameF >
inline auto transform(
    F && f
) const

Monadic operation: transforms the value (const).

Parameters:

f Function to apply to value.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: expected with transformed value or error.

function transform¶

template <typenameF >
inline auto transform(
    F && f
)

Monadic operation: transforms the value (rvalue).

Parameters:

f Function to apply to value.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: expected with transformed value or error.

function transform_error¶

template <typenameF >
inline auto transform_error(
    F && f
)

Monadic operation: transforms the error.

Parameters:

f Function to apply to error.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: expected with value or transformed error.

function transform_error¶

template <typenameF >
inline auto transform_error(
    F && f
) const

Monadic operation: transforms the error (const).

Parameters:

f Function to apply to error.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: expected with value or transformed error.

function transform_error¶

template <typenameF >
inline auto transform_error(
    F && f
)

Monadic operation: transforms the error (rvalue).

Parameters:

f Function to apply to error.

Exceptions:

None.

Template Parameters:

F Callable type.

Return: expected with value or transformed error.

function swap¶

inline void swap(
    expected & o
)

Swaps the contents with another expected.

Parameters:

o Expected to swap with.

Exceptions:

None if types are nothrow move constructible and swappable.

Since: 0.1

Note: None.

Warning: None.

Friends¶

friend operator==¶

friend constexprbool operator==(
    constexpected & a,

    constexpected< T2, E2 > & b
);

Equality comparison with another expected.

Parameters:

a First expected.
b Second expected.

Exceptions:

None.

Template Parameters:

T2 Other value type.
E2 Other error type.

Return: true if equal, false otherwise.

friend operator==¶

friend constexprbool operator==(
    constexpected & a,

    constT2 & v
);

Equality comparison with a value.

Parameters:

a Expected.
v Value to compare.

Exceptions:

None.

Template Parameters:

T2 Value type to compare with.

Return: true if expected contains value equal to v.

friend operator==¶

friend constexprbool operator==(
    constexpected & a,

    constunexpected< E2 > & u
);

Equality comparison with unexpected.

Parameters:

a Expected.
u Unexpected to compare.

Exceptions:

None.

Template Parameters:

E2 Error type of unexpected.

Return: true if expected contains matching error.

friend operator!=¶

friend constexprbool operator!=(
    constexpected & a,

    constexpected< T2, E2 > & b
);

Inequality comparison with another expected.

Parameters:

a First expected.
b Second expected.

Exceptions:

None.

Template Parameters:

T2 Other value type.
E2 Other error type.

Return: true if not equal, false otherwise.

friend operator!=¶

friend constexprbool operator!=(
    constexpected & a,

    constT2 & v
);

Inequality comparison with a value.

Parameters:

a Expected.
v Value to compare.

Exceptions:

None.

Template Parameters:

T2 Value type to compare with.

Return: true if not equal, false otherwise.

friend operator!=¶

friend constexprbool operator!=(
    constexpected & a,

    constunexpected< E2 > & u
);

Inequality comparison with unexpected.

Parameters:

a Expected.
u Unexpected to compare.

Exceptions:

None.

Template Parameters:

E2 Error type of unexpected.

Return: true if not equal, false otherwise.

friend swap¶

friend void swap(
    expected & a,

    expected & b
);

Non-member swap function.

Parameters:

a First expected.
b Second expected.

Exceptions:

None if types are nothrow move constructible and swappable.

Since: 0.1

Note: None.

Warning: None.

Updated on 2026-03-09 at 10:14:00 +0000