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[ostream.manip] Introduce SYNCBUF to detect basic_syncbuf LWG 3501 #4300

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[ostream.manip] Introduce SYNCBUF to detect basic_syncbuf LWG 3501 #4300

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48 changes: 30 additions & 18 deletions source/iostreams.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -6771,6 +6771,24 @@
specified in this subclause
is a designated addressable function\iref{namespace.std}.

\pnum
In this subclause,
\exposid{SYNCBUF}\tcode{(p)} for a pointer \tcode{p} of type \tcode{B*}
is determined as follows.
If \tcode{*p} is a base class subobject of an object of type \tcode{S},
where \tcode{S} is a specialization generated from
the \tcode{basic_syncbuf} primary template,
and \tcode{is_convertible_v<S*, B*>} is \tcode{true},
then \exposid{SYNCBUF}\tcode{(p)} is \tcode{dynamic_cast<S*>(p)}.
Otherwise, \exposid{SYNCBUF}\tcode{(p)} is \tcode{static_cast<void*>(nullptr)}.

\begin{note}
To work around the issue that the
\tcode{Allocator} template argument of \tcode{S} cannot be deduced,
implementations can introduce an intermediate base class
to \tcode{basic_syncbuf} that manages its \tcode{emit_on_sync} flag.
\end{note}

\indexlibraryglobal{endl}%
\begin{itemdecl}
template<class charT, class traits>
Expand Down Expand Up @@ -6832,19 +6850,13 @@
\end{itemdecl}

\begin{itemdescr}
\pnum
Let \tcode{p} be \exposid{SYNCBUF}\tcode{(os.rdbuf())}.

\pnum
\effects
If \tcode{os.rdbuf()} is a
\tcode{basic_syncbuf<charT, traits, Allocator>*},
called \tcode{buf} for the purpose of exposition,
calls \tcode{buf->set_emit_on_sync(true)}.
If \tcode{p} is not null, calls \tcode{p->set_emit_on_sync(true)}.
Otherwise this manipulator has no effect.
\begin{note}
To work around the issue that the
\tcode{Allocator} template argument cannot be deduced,
implementations can introduce an intermediate base class
to \tcode{basic_syncbuf} that manages its \tcode{emit_on_sync} flag.
\end{note}

\pnum
\returns
Expand All @@ -6858,12 +6870,12 @@
\end{itemdecl}

\begin{itemdescr}
\pnum
Let \tcode{p} be \exposid{SYNCBUF}\tcode{(os.rdbuf())}.

\pnum
\effects
If \tcode{os.rdbuf()} is a
\tcode{basic_syncbuf<charT, traits, Allocator>*},
called \tcode{buf} for the purpose of exposition,
calls \tcode{buf->set_emit_on_sync(false)}.
If \tcode{p} is not null, calls \tcode{p->set_emit_on_sync(false)}.
Otherwise this manipulator has no effect.

\pnum
Expand All @@ -6878,13 +6890,13 @@
\end{itemdecl}

\begin{itemdescr}
\pnum
Let \tcode{p} be \exposid{SYNCBUF}\tcode{(os.rdbuf())}.

\pnum
\effects
Calls \tcode{os.flush()}.
Then, if \tcode{os.rdbuf()} is a
\tcode{basic_syncbuf<charT, traits, Allocator>*},
called \tcode{buf} for the purpose of exposition,
calls \tcode{buf->emit()}.
If \tcode{p} is not null, calls \tcode{p->emit()}.

\pnum
\returns
Expand Down