Merge 2018-06 LWG Motion 17

Fixes #2134

Author: zygoloid

source/iostreams.tex

@@ -1655,15 +1655,37 @@
 \pnum
 \indexlibrary{\idxcode{fpos}}%
 \indexlibrary{\idxcode{streamoff}}%
-Operations specified in \tref{iostreams.position.requirements} are permitted.
+An \tcode{fpos} type specifies file position information.
+It holds a state object
+whose type is equal to the template parameter \tcode{stateT}.
+Type \tcode{stateT} shall meet
+the \tcode{DefaultConstructible} (\tref{defaultconstructible}),
+\tcode{CopyConstructible} (\tref{copyconstructible}),
+\tcode{CopyAssignable} (\tref{copyassignable}), and
+\tcode{Destructible} (\tref{destructible}) requirements.
+If \tcode{is_trivially_copy_constructible_v<stateT>} is \tcode{true},
+then \tcode{fpos<stateT>} has a trivial copy constructor.
+If \tcode{is_trivially_copy_assignable<stateT>} is \tcode{true},
+then \tcode{fpos<stateT>} has a trivial copy assignment operator.
+If \tcode{is_trivially_destructible_v<stateT>} is \tcode{true},
+then \tcode{fpos<stateT>} has a trivial destructor.
+All specializations of \tcode{fpos} satisfy
+the \tcode{DefaultConstructible},
+\tcode{CopyConstructible},
+\tcode{CopyAssignable},
+\tcode{Destructible},
+and \tcode{EqualityComparable} (\tref{equalitycomparable}) requirements.
+In addition, the expressions shown in \tref{iostreams.position.requirements}
+are valid and have the indicated semantics.
 In that table,
 \begin{itemize}
 \item \tcode{P} refers to an instance of \tcode{fpos},
-\item \tcode{p} and \tcode{q} refer to values of type \tcode{P},
-\item \tcode{O} refers to type \tcode{streamoff},
-\item \tcode{o} refers to a value of type \tcode{streamoff},
-\item \tcode{sz} refers to a value of type \tcode{streamsize} and
-\item \tcode{i} refers to a value of type \tcode{int}.
+\item \tcode{p} and \tcode{q} refer to values
+of type \tcode{P} or \tcode{const P},
+\item \tcode{pl} and \tcode{ql} refer to modifiable lvalues of type \tcode{P},
+\item \tcode{O} refers to type \tcode{streamoff}, and
+\item \tcode{o} refers to a value
+of type \tcode{streamoff} or \tcode{const streamoff}.
 \end{itemize}
 
 \begin{libreqtab4c}
@@ -1678,65 +1700,59 @@
 \lhdr{Expression}   & \chdr{Return type}  & \chdr{Operational}  & \rhdr{Assertion/note}   \\
             &           & \chdr{semantics}  & \rhdr{pre-/post-condition} \\ \capsep
 \endhead
-\tcode{P(i)}      &
-            &
-            &
- \tcode{p == P(i)}\br
- note: a destructor is assumed. \\ \rowsep
-\tcode{P p(i);}\br
-\tcode{P p = i;}    &
-            &
-            &
- \postconditions \tcode{p == P(i)}. \\ \rowsep
 \tcode{P(o)}      &
- \tcode{fpos}     &
- converts from \tcode{offset} & \\ \rowsep
+ \tcode{P}     &
+ converts from \tcode{offset} &
+ \effects Value-initializes the state object. \\ \rowsep
+\tcode{P p(o);}\br
+\tcode{P p = o;} &
+ &
+ &
+ \effects Value-initializes the state object. \br
+ \postconditions \tcode{p == P(o)} \\ \rowsep
+\tcode{P()} &
+ \tcode{P} &
+ \tcode{P(0)} &
+  \\ \rowsep
+\tcode{P p;} &
+ &
+ \tcode{P p(0);} &
+  \\ \rowsep
 \tcode{O(p)}      &
  \tcode{streamoff}      &
  converts to \tcode{offset} &
  \tcode{P(O(p)) == p} \\ \rowsep
-\tcode{p == q}      &
- convertible to \tcode{bool}  &
-            &
- \tcode{==} is an equivalence relation  \\ \rowsep
 \tcode{p != q}      &
  convertible to \tcode{bool}  &
  \tcode{!(p == q)}    & \\ \rowsep
-\tcode{q = p + o}\br
-\tcode{p += o}      &
- \tcode{fpos}     &
+\tcode{p + o} &
+ \tcode{P}     &
  \tcode{+} offset   &
- \tcode{q - o == p}   \\ \rowsep
-\tcode{q = p - o}\br
-\tcode{p -= o}      &
- \tcode{fpos}     &
+ \remarks With \tcode{ql = p + o;}, then: \tcode{ql - o == p}  \\ \rowsep
+\tcode{pl += o} &
+ \tcode{P\&} &
+ \tcode{+=} offset &
+ \remarks With \tcode{ql = pl;} before the \tcode{+=}, then:
+   \tcode{pl - o == ql} \\ \rowsep
+\tcode{p - o} &
+ \tcode{P}     &
  \tcode{-} offset   &
- \tcode{q + o == p}   \\ \rowsep
-\tcode{o = p - q}   &
+ \remarks With \tcode{ql = p - o;}, then: \tcode{ql + o == p}  \\ \rowsep
+\tcode{pl -= o} &
+ \tcode{P\&} &
+ \tcode{-=} offset &
+ \remarks With \tcode{ql = pl;} before the \tcode{-=}, then:
+    \tcode{pl + o == ql} \\ \rowsep
+\tcode{o + p} &
+ convertible to \tcode{P} &
+ \tcode{p + o} &
+ \tcode{P(o + p) == p + o} \\ \rowsep
+\tcode{p - q}   &
  \tcode{streamoff}      &
  distance       &
- \tcode{q + o == p}   \\ \rowsep
-\tcode{streamsize(o)}\br
-\tcode{O(sz)}     &
- \tcode{streamsize}\br
- \tcode{streamoff}      &
- converts\br
- converts       &
- \tcode{streamsize(O(sz)) == sz}\br
- \tcode{streamsize(O(sz)) == sz}  \\
+ \tcode{p == q + (p - q)}   \\ \rowsep
 \end{libreqtab4c}
 
-\pnum
-\begin{note}
-Every implementation is required to supply overloaded operators on
-\tcode{fpos}
-objects to satisfy the requirements of~\ref{fpos.operations}.
-It is unspecified whether these operators are members of
-\tcode{fpos},
-global operators,
-or provided in some other way.
-\end{note}
-
 \pnum
 Stream operations that return a value of type
 \tcode{traits::pos_type}