Add changes, reference; fix trailing whitespace

doc/system/acknowledgements.adoc

@@ -11,9 +11,9 @@ http://www.boost.org/LICENSE_1_0.txt
 # Acknowledgments
 :idprefix: ack_
 
-Christopher Kohlhoff and Peter Dimov made important contributions to the 
-design. Comments and suggestions were also received from Pavel Vozenilek, 
-Gennaro Prota, Dave Abrahams, Jeff Garland, Iain Hanson, Oliver Kowalke, and 
+Christopher Kohlhoff and Peter Dimov made important contributions to the
+design. Comments and suggestions were also received from Pavel Vozenilek,
+Gennaro Prota, Dave Abrahams, Jeff Garland, Iain Hanson, Oliver Kowalke, and
 Oleg Abrosimov. Christopher Kohlhoff suggested several improvements to the
 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2066.html[N2066]
 paper. Johan Nilsson's comments led to several of the refinements in N2066.

doc/system/changes.adoc

@@ -9,16 +9,51 @@ http://www.boost.org/LICENSE_1_0.txt
 
 [#changes]
 # Release History
-:idprefix: changes_
+:idprefix:
 
 ## Changes in Boost 1.69
 
-...
+* Boost.System is now header-only. A stub library is still built for
+  compatibility, but linking to it is no longer necessary.
+* Even more functions have been marked `constexpr`.
+* The destructor of `error_category` is now protected and no longer
+  virtual. This is a _potentially breaking change_ but its impact
+  is expected to be limited.
+* `error_category` now has a constructor that accepts a 64 bit identifier,
+  enabling distinct category objects to compare equal.
+* The constructors of `error_category` are now protected.
+* A non-allocating, nonthrowing overload of `message` has been added.
+* A virtual function `failed` has been added, allowing categories for
+  which success is not synonymous with 0.
+* The deprecated `boost::system::throws` object has been removed.
+* `boost::throws()` is now deprecated and its use is discouraged.
 
 ## Changes in Boost 1.68
 
-...
+On a {cpp}14 compiler, many Boost.System functions and member functions
+are now `constexpr`, and `error_code` and `error_condition` are literal
+classes.
+
+In addition to enabling use in constant expressions (and `constexpr`
+functions), this significantly improves the quality of the generated code.
+
+As a result of this change, however, now using Boost.System from {cpp}14
+or {cpp}17 code requires that the library is also built with {cpp}14 or
+above. This is the default on GCC 6 and newer, but not on GCC 5 or Clang.
+One can build Boost for {cpp}14 by passing the `cxxstd=14` option to `b2`.
+
+(Previous versions allowed code built against any {cpp} standard to link
+with Boost.System built against any {cpp} standard. In 1.68, code using
+any {cpp} standard can link with Boost.System built with {cpp}14 or above,
+but if Boost.System is built with {cpp}11 or below, only code also built
+with {cpp}11 and below can link to it successfully.)
 
 ## Changes in Boost 1.65
 
-...
+On a {cpp}11 compiler, Boost.System now provides implicit conversions
+from `boost::system::error_category`, `error_code`, and `error_condition`
+to their standard equivalents from `<system_error>`.
+
+This allows libraries to expose a {cpp}11 interface and report errors
+via `std::error_code` even when using Boost.System, directly or through a
+dependency such as Boost.ASIO.

doc/system/history.adoc

@@ -12,19 +12,19 @@ http://www.boost.org/LICENSE_1_0.txt
 :idprefix: history_
 
 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1975.html[N1975],
-Filesystem Library Proposal for TR2, accepted for Library Technical 
-Report 2 (TR2) at the Berlin meeting, included additional components to 
-supplement the Standard Library's Diagnostics clause. Since then, these error 
-reporting components have received wider public scrutiny and enhancements have 
+Filesystem Library Proposal for TR2, accepted for Library Technical
+Report 2 (TR2) at the Berlin meeting, included additional components to
+supplement the Standard Library's Diagnostics clause. Since then, these error
+reporting components have received wider public scrutiny and enhancements have
 been made to the design. The enhanced version has been used by
 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2054.pdf[N2054],
 Networking  Library Proposal for TR2, demonstrating that these error reporting
 components are useful beyond the original Filesystem Library.
 
 The original proposal viewed error categories as a binary choice between
-`errno` (i.e. POSIX-style) and the native operating system's error 
-codes. The proposed components now allow as many additional error categories as 
-are needed by either implementations or by users. The need to support additional 
-error categories, for example, occurs in some networking library implementations 
-because they are built on top of the POSIX `getaddrinfo` API that 
+`errno` (i.e. POSIX-style) and the native operating system's error
+codes. The proposed components now allow as many additional error categories as
+are needed by either implementations or by users. The need to support additional
+error categories, for example, occurs in some networking library implementations
+because they are built on top of the POSIX `getaddrinfo` API that
 uses error codes not based on `errno`.

doc/system/introduction.adoc

@@ -45,5 +45,6 @@ platforms other than their intended target.
 
 Boost.System is part of the {cpp}11 Standard Library.
 A number of changes, particularly to names, were made by the C++ committee
-during standardization. The Boost implementation has been tracking those changes. 
-See _Deprecated names_ for synonyms provided to prevent breakage of existing user code.
+during standardization. The Boost implementation has been tracking those changes.
+See <<#ref_deprecated_names,Deprecated Names>> for synonyms provided to prevent
+breakage of existing user code.

doc/system/rationale.adoc

@@ -11,15 +11,15 @@ http://www.boost.org/LICENSE_1_0.txt
 # Design Rationale
 :idprefix: rationale_
 
-`error_code` and `error_condition` are designed as a value types so 
+`error_code` and `error_condition` are designed as value types so
 they can be copied without slicing and do not requiring heap allocation, but
 still have polymorphic behavior based on the error category. This is achieved
 by abstract base class `error_category` supplying the polymorphic behavior,
 and `error_code` and `error_condition` containing a pointer to an object of a
 type derived from `error_category`.
 
-Many of the detailed design decisions were driven by the requirements that 
-users to be able to add additional error categories, and that it be no more 
+Many of the detailed design decisions were driven by the requirements that
+users to be able to add additional error categories, and that it be no more
 difficult to write portable code than system-specific code.
 
 The `operator<<` overload for `error_code` eliminates a misleading conversion to

doc/system/reference.adoc

@@ -12,24 +12,890 @@ http://www.boost.org/LICENSE_1_0.txt
 # Reference
 :idprefix: ref_
 
+## Use of {cpp}11 and {cpp}14 Features
+
+The library is documented to use several {cpp}11 and {cpp}14 features,
+including `noexcept`, explicit conversion operators and `constexpr`. The
+actual implementation uses {cpp}11 and {cpp}14 features only when they are
+available, and otherwise falls back on {cpp}03 features.
+
+## Macros
+
+When `BOOST_SYSTEM_ENABLE_DEPRECATED` is defined, the library provides
+deprecated features for compatibility. These features are bound to eventually
+disappear.
+
+When `BOOST_SYSTEM_USE_UTF8` is defined, on Windows the library returns
+UTF-8 messages using code page `CP_UTF8` instead of the default `CP_ACP`.
+This macro has no effect on POSIX.
+
+## Deprecated Names
+
+In the process of adding Boost.System to the {cpp}11 standard library, the
+{cpp} committee changed some names. To ease transition, Boost.System deprecates
+the old names, but will provide them when the macro `BOOST_SYSTEM_ENABLE_DEPRECATED` is defined.
+
+|===
+|Old usage, now deprecated|Replacement
+
+|`get_generic_category()`|`generic_category()`
+|`get_system_category()`|`system_category()`
+|`namespace posix`|`namespace errc`
+|`namespace posix_error`|`namespace errc`
+|`get_posix_category()`|`generic_category()`
+|`posix_category`|`generic_category()`
+|`errno_ecat`|`generic_category()`
+|`native_ecat`|`system_category()`
+|===
+
 ## <boost/system/error_code.hpp>
 
 ### Synopsis
 
-...
+```
+namespace boost {
+  namespace system {
 
-### error_category
+    class error_category;
 
-...
+    constexpr const error_category & system_category() noexcept;
+    constexpr const error_category & generic_category() noexcept;
 
-### error_code
+    class error_code;
+    class error_condition;
 
-...
+    // "Concept" helpers
 
-### error_condition
+    template<class T>
+      struct is_error_code_enum { static const bool value = false; };
 
-...
+    template<class T>
+      struct is_error_condition_enum { static const bool value = false; };
+
+    // generic error conditions
+
+    namespace errc {
+      enum errc_t
+      {
+        success = 0,
+        address_family_not_supported,   //EAFNOSUPPORT
+        address_in_use,                 //EADDRINUSE
+        address_not_available,          //EADDRNOTAVAIL
+        already_connected,              //EISCONN
+        argument_list_too_long,         //E2BIG
+        argument_out_of_domain,         //EDOM
+        bad_address,                    //EFAULT
+        bad_file_descriptor,            //EBADF
+        bad_message,                    //EBADMSG
+        broken_pipe,                    //EPIPE
+        connection_aborted,             //ECONNABORTED
+        connection_already_in_progress, //EALREADY
+        connection_refused,             //ECONNREFUSED
+        connection_reset,               //ECONNRESET
+        cross_device_link,              //EXDEV
+        destination_address_required,   //EDESTADDRREQ
+        device_or_resource_busy,        //EBUSY
+        directory_not_empty,            //ENOTEMPTY
+        executable_format_error,        //ENOEXEC
+        file_exists,                    //EEXIST
+        file_too_large,                 //EFBIG
+        filename_too_long,              //ENAMETOOLONG
+        function_not_supported,         //ENOSYS
+        host_unreachable,               //EHOSTUNREACH
+        identifier_removed,             //EIDRM
+        illegal_byte_sequence,          //EILSEQ
+        inappropriate_io_control_operation, //ENOTTY
+        interrupted,                    //EINTR
+        invalid_argument,               //EINVAL
+        invalid_seek,                   //ESPIPE
+        io_error,                       //EIO
+        is_a_directory,                 //EISDIR
+        message_size,                   //EMSGSIZE
+        network_down,                   //ENETDOWN
+        network_reset,                  //ENETRESET
+        network_unreachable,            //ENETUNREACH
+        no_buffer_space,                //ENOBUFS
+        no_child_process,               //ECHILD
+        no_link,                        //ENOLINK
+        no_lock_available,              //ENOLCK
+        no_message_available,           //ENODATA
+        no_message,                     //ENOMSG
+        no_protocol_option,             //ENOPROTOOPT
+        no_space_on_device,             //ENOSPC
+        no_stream_resources,            //ENOSR
+        no_such_device_or_address,      //ENXIO
+        no_such_device,                 //ENODEV
+        no_such_file_or_directory,      //ENOENT
+        no_such_process,                //ESRCH
+        not_a_directory,                //ENOTDIR
+        not_a_socket,                   //ENOTSOCK
+        not_a_stream,                   //ENOSTR
+        not_connected,                  //ENOTCONN
+        not_enough_memory,              //ENOMEM
+        not_supported,                  //ENOTSUP
+        operation_canceled,             //ECANCELED
+        operation_in_progress,          //EINPROGRESS
+        operation_not_permitted,        //EPERM
+        operation_not_supported,        //EOPNOTSUPP
+        operation_would_block,          //EWOULDBLOCK
+        owner_dead,                     //EOWNERDEAD
+        permission_denied,              //EACCES
+        protocol_error,                 //EPROTO
+        protocol_not_supported,         //EPROTONOSUPPORT
+        read_only_file_system,          //EROFS
+        resource_deadlock_would_occur,  //EDEADLK
+        resource_unavailable_try_again, //EAGAIN
+        result_out_of_range,            //ERANGE
+        state_not_recoverable,          //ENOTRECOVERABLE
+        stream_timeout,                 //ETIME
+        text_file_busy,                 //ETXTBSY
+        timed_out,                      //ETIMEDOUT
+        too_many_files_open_in_system,  //ENFILE
+        too_many_files_open,            //EMFILE
+        too_many_links,                 //EMLINK
+        too_many_synbolic_link_levels,  //ELOOP
+        value_too_large,                //EOVERFLOW
+        wrong_protocol_type             //EPROTOTYPE
+      };
+
+    } // namespace errc
+
+    template<> struct is_error_condition_enum<errc::errc_t>
+      { static const bool value = true; };
+
+    // non-member functions
+
+    constexpr bool operator==( const error_code & lhs,
+      const error_code & rhs ) noexcept;
+    bool operator==( const error_code & code,
+      const error_condition & condition ) noexcept;
+    bool operator==( const error_condition & condition,
+      const error_code & code ) noexcept;
+    constexpr bool operator==( const error_condition & lhs,
+      const error_condition & rhs ) noexcept;
+
+    constexpr bool operator!=( const error_code & lhs,
+      const error_code & rhs ) noexcept;
+    bool operator!=( const error_code & code,
+      const error_condition & condition ) noexcept;
+    bool operator!=( const error_condition & condition,
+      const error_code & code ) noexcept;
+    constexpr bool operator!=( const error_condition & lhs,
+      const error_condition & rhs ) noexcept;
+
+    constexpr bool operator<( const error_code & lhs,
+      const error_code & rhs ) noexcept;
+    constexpr bool operator<( const error_condition & lhs,
+      const error_condition & rhs ) noexcept;
+
+    constexpr error_code make_error_code( errc::errc_t e ) noexcept;
+    constexpr error_condition make_error_condition( errc::errc_t e ) noexcept;
+
+    template <class charT, class traits>
+      std::basic_ostream<charT, traits>&
+        operator<<( basic_ostream<charT, traits>& os, const error_code & ec );
+
+    std::size_t hash_value( const error_code & ec );
+
+  } // namespace system
+
+  system::error_code & throws();
+
+} // namespace boost
+```
+
+The value of each `errc_t` constant is the same as the value of the `<cerrno>`
+macro shown in the above synopsis.
+
+Users may specialize `is_error_code_enum` and `is_error_condition_enum`
+templates to indicate that a type is eligible for class `error_code` and
+`error_condition` automatic conversions respectively.
+
+### Class error_category
+
+The class `error_category` defines the base class for types used
+to identify the source and encoding of a particular category of error code.
+
+Classes may be derived from `error_category` to support categories of
+errors in addition to those defined in Boost.System.
+
+```
+namespace boost {
+  namespace system {
+
+    class error_category
+    {
+    public: // noncopyable
+
+      error_category( error_category const & ) = delete;
+      error_category& operator=( error_category const & ) = delete;
+
+    protected:
+
+      ~error_category() = default;
+
+      constexpr error_category() noexcept;
+      explicit constexpr error_category( unsigned long long id ) noexcept;
+
+    public:
+
+      virtual const char * name() const noexcept = 0;
+
+      virtual error_condition default_error_condition( int ev ) const noexcept;
+
+      virtual bool equivalent( int code, const error_condition & condition )
+        const noexcept;
+      virtual bool equivalent( const error_code & code, int condition )
+        const noexcept;
+
+      virtual std::string message( int ev ) const = 0;
+      virtual char const * message( int ev, char * buffer, std::size_t len )
+        const noexcept;
+
+      virtual bool failed( int ev ) const noexcept;
+
+      constexpr bool operator==( const error_category & rhs ) const noexcept;
+      constexpr bool operator!=( const error_category & rhs ) const noexcept;
+      constexpr bool operator< ( const error_category & rhs ) const noexcept;
+
+      operator std::error_category const & () const;
+
+    private:
+
+      unsigned long long id_; // exposition only
+
+    };
+  }
+}
+```
+
+#### Constructors
+
+```
+constexpr error_category() noexcept;
+```
+[none]
+* {blank}
++
+Effects: :: Initializes `id_` to 0.
+Remarks: :: Since equivalence for categories that do not have an identifier is
+  based on comparing object addresses, a user-defined derived category of type
+  `C` that uses this constructor should ensure that only one object of type `C`
+  exists in the program.
+
+```
+explicit constexpr error_category( unsigned long long id ) noexcept;
+```
+[none]
+* {blank}
++
+Effects: :: Initializes `id_` to `id`.
+Remarks: :: User-defined derived categories that use this constructor are considered
+  equivalent when their identifiers match. Therefore, those categories may have more
+  than one instance existing in a program, but to minimize the possibility of
+  collision, their identifiers must be randomly chosen (at the time the category
+  is implemented, not at runtime). One way of generating a 64 bit random identifier
+  is https://www.random.org/cgi-bin/randbyte?nbytes=8&format=h.
+
+#### Virtuals
+
+```
+virtual const char * name() const noexcept = 0;
+```
+[none]
+* {blank}
++
+Returns: :: In derived classes, a character literal naming the error category.
+
+```
+virtual error_condition default_error_condition( int ev ) const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+- In derived classes, an error condition corresponding to `ev`.
+  The returned error condition will typically come from the generic category.
+- In the default implementation, `error_condition( ev, *this )`.
+
+```
+virtual bool equivalent( int code, const error_condition & condition )
+  const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+- In derived classes, `true` when `error_code( code, *this )` is equivalent to `condition`.
+- In the default implementation, `default_error_condition( code ) == condition`.
+
+```
+virtual bool equivalent( const error_code & code, int condition )
+  const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+- In derived classes, `true` when `code` is equivalent to `error_condition( condition, *this )`.
+- In the default implementation, `*this == code.category() && code.value() == condition`.
+
+```
+virtual std::string message( int ev ) const = 0;
+```
+[none]
+* {blank}
++
+Returns: :: In derived classes, a string that describes the error denoted by `ev`.
+
+```
+virtual char const * message( int ev, char * buffer, std::size_t len )
+  const noexcept;
+```
+[none]
+* {blank}
++
+Effects: ::
+** Derived classes should either
+  *** return a pointer to a character literal describing the error denoted by `ev`, or
+  *** copy a string describing the error into `buffer`, truncating it to `len-1`
+      characters and storing a null terminator, and return `buffer`. If `len` is 0,
+      nothing is copied, but the function still returns `buffer`. Note that
+      when `len` is 0, `buffer` may be `nullptr`.
+** The default implementation calls `message(ev)` and copies the result into
+   `buffer`, truncating it to `len-1` characters and storing a null terminator.
+   If `len` is 0, copies nothing. Returns `buffer`. If `message(ev)` throws an
+   exception, the string `"Message text unavailable"` is used.
+
+```
+virtual bool failed( int ev ) const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+- In derived classes, `true` when `ev` represents a failure.
+- In the default implementation, `ev != 0`.
+Remarks: ::
+  All calls to this function with the same `ev` must return the same value.
+
+#### Nonvirtuals
+
+```
+constexpr bool operator==( const error_category & rhs ) const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `rhs.id_ == 0? this == &rhs: id_ == rhs.id_`.
+Remarks: :: Two category objects are considered equivalent when they have matching
+  nonzero identifiers, or are the same object.
+
+```
+constexpr bool operator!=( const error_category & rhs ) const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `!( *this == rhs )`.
+
+```
+constexpr bool operator< ( const error_category & rhs ) const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+** If `id_ < rhs.id_`, `true`;
+** Otherwise, if `id_ > rhs.id_`, `false`;
+** Otherwise, if `rhs.id_ != 0`, `false`;
+** Otherwise, `std::less<error_category const *>()( this, &rhs )`.
+
+```
+operator std::error_category const & () const;
+```
+[none]
+* {blank}
++
+Returns: :: A reference to an `std::error_category` object corresponding
+  to `*this`.
+
+### Predefined Categories
+
+```
+constexpr const error_category & system_category() noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: A reference to an `error_category` object identifying errors
+  originating from the operating system.
+
+```
+constexpr const error_category & generic_category() noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: A reference to an `error_category` object identifying portable
+  error conditions.
+
+### Class error_code
+
+The class `error_code` describes an object used to hold error code
+values, such as those originating from the operating system or other
+low-level application program interfaces. It's an adjunct to error reporting
+by exception.
+
+```
+namespace boost {
+  namespace system {
+
+    class error_code {
+    public:
+
+      // constructors:
+
+      constexpr error_code() noexcept;
+      constexpr error_code( int val, const error_category & cat ) noexcept;
+
+      template <class ErrorCodeEnum>
+        constexpr error_code( ErrorCodeEnum e ) noexcept;
+
+      // modifiers:
+
+      constexpr void assign( int val, const error_category & cat ) noexcept;
+
+      template<typename ErrorCodeEnum>
+        constexpr error_code & operator=( ErrorCodeEnum e ) noexcept;
+
+      constexpr void clear() noexcept;
+
+      // observers:
+
+      constexpr int value() const noexcept;
+      constexpr const error_category & category() const noexcept;
+
+      error_condition default_error_condition() const noexcept;
+
+      std::string message() const;
+      char const * message( char * buffer, std::size_t len ) const noexcept;
+
+      constexpr bool failed() const noexcept;
+      constexpr explicit operator bool() const noexcept;
+
+      operator std::error_code() const;
+
+    private: // exposition only
+
+      int val_;
+      const error_category * cat_;
+
+    };
+  }
+}
+```
+
+#### Constructors
+
+```
+constexpr error_code() noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `val_ == 0`; `*cat_ == system_category()`.
+
+```
+constexpr error_code( int val, const error_category & cat ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `val_ == val`; `cat_ == &cat`.
+
+```
+template <class ErrorCodeEnum>
+  constexpr error_code( ErrorCodeEnum e ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `*this == make_error_code( e )`.
+Remarks: :: This constructor is only enabled when `is_error_code_enum<ErrorCodeEnum>::value` is `true`.
+
+#### Modifiers
+
+```
+constexpr void assign( int val, const error_category & cat ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `val_ == val`; `cat_ == &cat`.
+
+```
+template<typename ErrorCodeEnum>
+  constexpr error_code & operator=( ErrorCodeEnum e ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `*this == make_error_code( e )`.
+Remarks: :: This operator is only enabled when `is_error_code_enum<ErrorCodeEnum>::value` is `true`.
+
+```
+constexpr void clear() noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `val_ == 0`; `*cat_ == system_category()`.
+
+#### Observers
+
+```
+constexpr int value() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `val_`.
+
+```
+constexpr const error_category & category() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `*cat_`.
+
+```
+error_condition default_error_condition() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `cat_\->default_error_condition( val_ )`.
+
+```
+std::string message() const;
+```
+[none]
+* {blank}
++
+Returns: :: `cat_\->message( val_ )`.
+
+```
+char const * message( char * buffer, std::size_t len ) const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `cat_\->message( val_, buffer, len )`.
+
+```
+constexpr bool failed() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `cat_\->failed( val_ )`.
+
+```
+constexpr explicit operator bool() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `failed()`.
+
+```
+operator std::error_code() const;
+```
+[none]
+* {blank}
++
+Returns: :: `std::error_code( val_, *cat_ )`.
+
+### Class error_condition
+
+```
+namespace boost {
+  namespace system {
+
+    class error_condition {
+    public:
+
+      // constructors:
+
+      constexpr error_condition() noexcept;
+      constexpr error_condition( int val, const error_category & cat ) noexcept;
+
+      template <class ErrorConditionEnum>
+        constexpr error_condition( ErrorConditionEnum e ) noexcept;
+
+      // modifiers:
+
+      constexpr void assign( int val, const error_category & cat ) noexcept;
+
+      template<typename ErrorConditionEnum>
+        constexpr error_condition & operator=( ErrorConditionEnum e ) noexcept;
+
+      constexpr void clear() noexcept;
+
+      // observers:
+
+      constexpr int value() const noexcept;
+      constexpr const error_category & category() const noexcept;
+
+      std::string message() const;
+      char const * message( char * buffer, std::size_t len ) const noexcept;
+
+      constexpr bool failed() const noexcept;
+      constexpr explicit operator bool() const noexcept;
+
+      operator std::error_condition() const;
+
+    private: // exposition only
+
+      int val_;
+      const error_category * cat_;
+
+    };
+  }
+}
+```
+
+#### Constructors
+
+```
+constexpr error_condition() noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `val_ == 0`; `*cat_ == generic_category()`.
+
+```
+constexpr error_condition( int val, const error_category & cat ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `val_ == val`; `cat_ == &cat`.
+
+```
+template <class ErrorConditionEnum>
+  constexpr error_condition( ErrorConditionEnum e ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `*this == make_error_condition( e )`.
+Remarks: :: This constructor is only enabled when `is_error_condition_enum<ErrorConditionEnum>::value` is `true`.
+
+#### Modifiers
+
+```
+constexpr void assign( int val, const error_category & cat ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `val_ == val`; `cat_ == &cat`.
+
+```
+template <class ErrorConditionEnum>
+  constexpr error_condition & operator=( ErrorConditionEnum e ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `*this == make_error_condition( e )`.
+Remarks: :: This operator is only enabled when `is_error_condition_enum<ErrorConditionEnum>::value` is `true`.
+
+```
+constexpr void clear() noexcept;
+```
+[none]
+* {blank}
++
+Ensures: :: `val_ == 0`; `*cat_ == generic_category()`.
+
+#### Observers
+
+```
+constexpr int value() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `val_`.
+
+```
+constexpr const error_category & category() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `*cat_`.
+
+```
+std::string message() const;
+```
+[none]
+* {blank}
++
+Returns: :: `cat_\->message( val_ )`.
+
+```
+char const * message( char * buffer, std::size_t len ) const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `cat_\->message( val_, buffer, len )`.
+
+```
+constexpr bool failed() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `cat_\->failed( val_ )`.
+
+```
+constexpr explicit operator bool() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `failed()`.
+
+```
+operator std::error_condition() const;
+```
+[none]
+* {blank}
++
+Returns: :: `std::error_condition( val_, *cat_ )`.
+
+### Nonmember functions
+
+```
+constexpr bool operator==( const error_code & lhs,
+  const error_code & rhs ) noexcept;
+constexpr bool operator==( const error_condition & lhs,
+  const error_condition & rhs ) noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `lhs.value() == rhs.value() && lhs.category() == rhs.category()`.
+
+```
+bool operator==( const error_code & code,
+  const error_condition & condition ) noexcept;
+bool operator==( const error_condition & condition,
+  const error_code & code ) noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `code.category().equivalent( code.value(), condition ) || condition.category().equivalent( code, condition.value() )`.
+
+```
+constexpr bool operator!=( const error_code & lhs,
+  const error_code & rhs ) noexcept;
+constexpr bool operator!=( const error_condition & lhs,
+  const error_condition & rhs ) noexcept;
+bool operator!=( const error_code & code,
+  const error_condition & condition ) noexcept;
+bool operator!=( const error_condition & condition,
+  const error_code & code ) noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `!( lhs == rhs )`.
+
+```
+constexpr bool operator<( const error_code & lhs,
+  const error_code & rhs ) noexcept;
+constexpr bool operator<( const error_condition & lhs,
+  const error_condition & rhs ) noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `lhs.category() < rhs.category() || ( lhs.category() == rhs.category() && lhs.value() < rhs.value() )`.
+
+```
+constexpr error_code make_error_code( errc::errc_t e ) noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `error_code( e, generic_category() )`.
+
+```
+constexpr error_condition make_error_condition( errc::errc_t e ) noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `error_condition( e, generic_category() )`.
+
+```
+template <class charT, class traits>
+  std::basic_ostream<charT, traits>&
+    operator<<( basic_ostream<charT, traits>& os, const error_code & ec );
+```
+[none]
+* {blank}
++
+Effects: :: `os << ec.category().name() << ':' << ec.value()`.
+Returns: :: `os`.
+
+```
+std::size_t hash_value( const error_code & ec );
+```
+[none]
+* {blank}
++
+Returns: :: A hash value representing `ec`.
 
 ## <boost/system/system_error.hpp>
 
-...
+### Class system_error
+
+The class `system_error` describes an exception object used to
+report errors that have an associated `error_code`. Such errors
+typically originate from operating system or other low-level
+application program interfaces.
+
+```
+namespace boost
+{
+  namespace system
+  {
+    class system_error: public std::runtime_error
+    {
+    public:
+
+      system_error( error_code ec );
+      system_error( error_code ec, const char * what_arg );
+      system_error( error_code ec, const std::string & what_arg );
+      system_error( int ev, const error_category & ecat,
+                    const char * what_arg );
+      system_error( int ev, const error_category & ecat,
+                    const std::string & what_arg );
+      system_error( int ev, const error_category & ecat );
+
+      const error_code & code() const noexcept;
+      const char * what() const noexcept;
+    };
+  }
+}
+```