API reference

Macros
1. Constrained template macros
2. Version macros
3. BOOST_OUTCOME_CO_TRY(var, expr)
  Evaluate within a coroutine an expression which results in an understood type, assigning T to a variable called var if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
4. BOOST_OUTCOME_CO_TRYV(expr)/BOOST_OUTCOME_CO_TRY(expr)
  Evaluate from within a coroutine an expression which results in an understood type, continuing execution if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
5. BOOST_OUTCOME_CO_TRYV_FAILURE_LIKELY(expr)/BOOST_OUTCOME_CO_TRY_FAILURE_LIKELY(expr)
  Evaluate from within a coroutine an expression which results in an understood type, continuing execution if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
6. BOOST_OUTCOME_CO_TRYX(expr)
  Evaluate from within a coroutine an expression which results in an understood type, emitting the T if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
7. BOOST_OUTCOME_CO_TRYX_FAILURE_LIKELY(expr)
  Evaluate from within a coroutine an expression which results in an understood type, emitting the T if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
8. BOOST_OUTCOME_CO_TRY_FAILURE_LIKELY(var, expr)
  Evaluate within a coroutine an expression which results in an understood type, assigning T to a variable called var if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
9. BOOST_OUTCOME_DISABLE_EXECINFO
  If defined, disables the use of the <execinfo.h> header (or the win32 emulation).
10. BOOST_OUTCOME_NODISCARD
  How to tell the compiler than the return value of a function should not be discarded without examining it.
11. BOOST_OUTCOME_REQUIRES(...)
  A C++ 20 requires(...), if available.
12. BOOST_OUTCOME_SYMBOL_VISIBLE
  How to mark throwable types as always having default ELF symbol visibility.
13. BOOST_OUTCOME_THREAD_LOCAL
  How to mark variables as having thread local storage duration.
14. BOOST_OUTCOME_THROW_EXCEPTION(expr)
  How to throw a C++ exception, or equivalent thereof.
15. BOOST_OUTCOME_TRY(var, expr)
  Evaluate an expression which results in an understood type, assigning T to a variable called var if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
16. BOOST_OUTCOME_TRYV(expr)/BOOST_OUTCOME_TRY(expr)
  Evaluate an expression which results in an understood type, continuing execution if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
17. BOOST_OUTCOME_TRYV_FAILURE_LIKELY(expr)/BOOST_OUTCOME_TRY_FAILURE_LIKELY(expr)
  Evaluate an expression which results in an understood type, continuing execution if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
18. BOOST_OUTCOME_TRYX(expr)
  Evaluate an expression which results in an understood type, emitting the T if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
19. BOOST_OUTCOME_TRYX_FAILURE_LIKELY(expr)
  Evaluate an expression which results in an understood type, emitting the T if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
20. BOOST_OUTCOME_TRY_FAILURE_LIKELY(var, expr)
  Evaluate an expression which results in an understood type, assigning T to a variable called var if successful, immediately returning try_operation_return_as(X) from the calling function if unsuccessful.
21. BOOST_OUTCOME_USE_STD_IN_PLACE_TYPE
  How to implement in_place_type_t<T> and in_place_type<T>.
22. BOOST_OUTCOME_USE_STD_IS_NOTHROW_SWAPPABLE
  How to implement is_nothrow_swappable<T>.
Concepts
1. ValueOrError<T, E>
  A boolean concept matching types with either a value or an error.
2. ValueOrNone<T>
  A boolean concept matching types with an optional value.
Converters
1. value_or_error<T, U>
  A customisable converter of ValueOrError<T, E> concept matching types.
Traits
1. is_basic_outcome<T>
  An integral constant type true for basic_outcome<T, EC, EP, NoValuePolicy> types.
2. is_basic_result<T>
  An integral constant type true for basic_result<T, E, NoValuePolicy> types.
3. is_error_code_available<T>
  True if an error code can be constructed from a T.
4. is_error_type<E>
  A customisable integral constant type true for E types which are to receive error throwing no-value policies.
5. is_error_type_enum<E, Enum>
  A customisable integral constant type true for E types constructible from Enum types which are to receive error throwing no-value policies.
6. is_exception_ptr_available<T>
  True if an exception ptr can be constructed from a T.
7. is_failure_type<T>
  An integral constant boolean variable true for failure_type<EC, E = void> types.
8. is_success_type<T>
  An integral constant boolean variable true for success_type<T> types.
9. type_can_be_used_in_basic_result<R>
  A constexpr boolean true for types permissible in basic_result<T, E, NoValuePolicy>.
Policies
1. base
  Base class of most policy classes defining the narrow observer policies.
2. all_narrow
  Policy class defining that hard undefined behaviour should occur on incorrect narrow and wide value, error or exception observation. Inherits publicly from base.
3. error_code_throw_as_system_error<T, EC, EP>
  Policy class defining that EP ought to be rethrown if possible, then the ADL discovered free function outcome_throw_as_system_error_with_payload() should be called on incorrect wide value observation. Inherits publicly from base. Can only be used with basic_outcome.
4. error_code_throw_as_system_error<T, EC, void>
  Policy class defining that the ADL discovered free function outcome_throw_as_system_error_with_payload() should be called on incorrect wide value observation. Inherits publicly from base. Can only be used with basic_result.
5. exception_ptr_rethrow<T, EC, EP>
  Policy class defining that the ADL discovered free function rethrow_exception() should be called on incorrect wide value observation. Inherits publicly from base. Can only be used with basic_outcome.
6. exception_ptr_rethrow<T, EC, void>
  Policy class defining that the ADL discovered free function rethrow_exception() should be called on incorrect wide value observation. Inherits publicly from base. Can only be used with basic_result.
7. fail_to_compile_observers
  Policy class defining that a static assertion should occur upon compilation of the wide value, error or exception observation. Inherits publicly from base.
8. terminate
  Policy class defining that std::terminate() should be called on incorrect wide value, error or exception observation. Inherits publicly from base.
9. throw_bad_result_access<EC>
  Policy class defining that bad_result_access_with<EC> should be thrown on incorrect wide value observation. Inherits publicly from base.
Types
1. basic_outcome<T, EC, EP, NoValuePolicy>
  A type carrying one of (i) a successful T (ii) a disappointment EC (iii) a failure EP (iv) both a disappointment EC and a failure EP, with NoValuePolicy specifying what to do if one tries to read state which isn’t there.
2. basic_result<T, E, NoValuePolicy>
  A sum type carrying either a successful T, or a disappointment E, with NoValuePolicy specifying what to do if one tries to read state which isn’t there.
3. bad_outcome_access
  Exception type publicly inheriting from std::logic_error indicating an incorrect observation of value or error or exception occurred.
4. bad_result_access_with<EC>
  Exception type publicly inheriting from bad_result_access indicating an incorrect observation of value occurred, supplying the error value.
5. bad_result_access
  Exception type publicly inheriting from std::logic_error indicating an incorrect observation of value or error occurred.
6. eager<T>/atomic_eager<T>
  An eagerly evaluated coroutine awaitable with Outcome customisation.
7. failure_type<EC, EP = void>
  Type sugar for constructing an unsuccessful result or outcome.
8. in_place_type_t<T>
  Either std::in_place_type_t<T> or a local emulation, depending on the BOOST_OUTCOME_USE_STD_IN_PLACE_TYPE macro.
9. lazy<T>/atomic_lazy<T>
  A lazily evaluated coroutine awaitable with Outcome customisation.
10. success_type<T>
  Type sugar for constructing a successful result or outcome.
Aliases
1. boost_checked<T, E = boost::system::error_code>
  A type alias to a basic_result configured with boost::system::error_code and policy::throw_bad_result_access<EC>.
2. boost_outcome<T, EC = boost::system::error_code, EP = boost::exception_ptr, NoValuePolicy = policy::default_policy<T, EC, EP>>
  A type alias to a basic_outcome configured with boost::system::error_code, boost::exception_ptr and policy::default_policy.
3. boost_result<T, E = boost::system::error_code, NoValuePolicy = policy::default_policy<T, E, void>>
  A type alias to a basic_result configured with boost::system::error_code and policy::default_policy.
4. boost_unchecked<T, E = boost::system::error_code>
  A type alias to a basic_result configured with boost::system::error_code and policy::all_narrow.
5. checked<T, E = varies>
  A type alias to a std_checked<T, E> (standalone edition) or boost_checked<T, E> (Boost edition).
6. default_policy<T, EC, EP>
  A type alias to a no-value policy selected based on traits matching of T, EC and EP.
7. outcome<T, EC = varies, EP = varies, NoValuePolicy = policy::default_policy<T, EC, EP>>
  A type alias to a std_outcome<T, EC, EP, NoValuePolicy> (standalone edition) or boost_outcome<T, EC, EP, NoValuePolicy> (Boost edition).
8. result<T, E = varies, NoValuePolicy = policy::default_policy<T, E, void>>
  A type alias to a std_result<T, E, NoValuePolicy> (standalone edition) or boost_result<T, E, NoValuePolicy> (Boost edition).
9. std_checked<T, E = std::error_code>
  A type alias to a basic_result configured with std::error_code and policy::throw_bad_result_access<EC>.
10. std_outcome<T, EC = std::error_code, EP = std::exception_ptr, NoValuePolicy = policy::default_policy<T, EC, EP>>
  A type alias to a basic_outcome configured with std::error_code, std::exception_ptr and policy::default_policy.
11. std_result<T, E = std::error_code, NoValuePolicy = policy::default_policy<T, E, void>>
  A type alias to a basic_result configured with std::error_code and policy::default_policy.
12. std_unchecked<T, E = std::error_code>
  A type alias to a basic_result configured with std::error_code and policy::all_narrow.
13. unchecked<T, E = varies>
  A type alias to a std_unchecked<T, E> (standalone edition) or boost_unchecked<T, E> (Boost edition).
Functions
1. Hooks
  Functions used to hook into the functionality of basic_result and basic_outcome.
2. Iostream
  Functions used to print, serialise and deserialise basic_result and basic_outcome.
3. Policy
  Functions used to customise how the policy classes operate.
4. auto failure(T &&, ...)
  Returns appropriate type sugar for constructing an unsuccessful result or outcome.
5. auto success(T &&)
  Returns appropriate type sugar for constructing a successful result or outcome.
6. bool try_operation_has_value(X)
  Default implementation of try_operation_has_value(X) ADL customisation point for BOOST_OUTCOME_TRY.
7. decltype(auto) try_operation_extract_value(X)
  Default implementation of try_operation_extract_value(X) ADL customisation point for BOOST_OUTCOME_TRY.
8. decltype(auto) try_operation_return_as(X)
  Default implementation of try_operation_return_as(X) ADL customisation point for BOOST_OUTCOME_TRY.
9. std::error_code error_from_exception(std::exception_ptr &&ep = std::current_exception(), std::error_code not_matched = std::make_error_code(std::errc::resource_unavailable_try_again)) noexcept
  Returns an error code matching a thrown standard library exception.
10. void strong_swap(bool &all_good, T &a, T &b)
  Tries to perform a strong guarantee swap.
11. void try_throw_std_exception_from_error(std::error_code ec, const std::string &msg = std::string{})
  Try to throw a standard library exception type matching an error code.