Merge 2018-03 LWG Motion 12

Author: zygoloid

source/future.tex

@@ -2550,6 +2550,36 @@
 The weak form may fail spuriously. See~\ref{atomics.types.operations}.
 \end{itemdescr}
 
+\rSec1[depr.string.capacity]{Deprecated \tcode{basic_string} capacity}
+
+\pnum
+The following member is declared in addition to those members specified
+in \ref{string.capacity}:
+
+\indexlibrary{\idxcode{basic_string}}%
+\begin{codeblock}
+namespace std {
+  template<class charT, class traits = char_traits<charT>,
+           class Allocator = allocator<charT>>
+  class basic_string {
+  public:
+    void reserve();
+  };
+}
+\end{codeblock}
+
+\indexlibrarymember{reserve}{basic_string}%
+\begin{itemdecl}
+void reserve();
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum\effects
+After this call, \tcode{capacity()} has an unspecified value
+greater than or equal to \tcode{size()}.
+\begin{note} This is a non-binding shrink to fit request. \end{note}
+\end{itemdescr}
+
 \rSec1[depr.locale.stdcvt]{Deprecated standard code conversion facets}
 
 \pnum

source/strings.tex

@@ -969,7 +969,7 @@
     void resize(size_type n, charT c);
     void resize(size_type n);
     size_type capacity() const noexcept;
-    void reserve(size_type res_arg = 0);
+    void reserve(size_type res_arg);
     void shrink_to_fit();
     void clear() noexcept;
     [[nodiscard]] bool empty() const noexcept;
@@ -1771,35 +1771,25 @@
 
 \indexlibrarymember{reserve}{basic_string}%
 \begin{itemdecl}
-void reserve(size_type res_arg=0);
+void reserve(size_type res_arg);
 \end{itemdecl}
 
 \begin{itemdescr}
-\pnum
-The member function
-\tcode{reserve()}
-is a directive that informs a
-\tcode{basic_string}
-object of a planned change in size,
-so that it can manage the storage allocation accordingly.
-
 \pnum
 \effects
+A directive that informs a \tcode{basic_string} of a planned change in size,
+so that the storage allocation can be managed accordingly.
 After
 \tcode{reserve()},
 \tcode{capacity()}
 is greater or equal to the argument of
-\tcode{reserve}.
-\begin{note}
-Calling
-\tcode{reserve()}
-with a \tcode{res_arg} argument less than
+\tcode{reserve}
+if reallocation happens; and
+equal to the previous value of
 \tcode{capacity()}
-is in effect a non-binding shrink request.
-A call with
-\tcode{res_arg <= size()}
-is in effect a non-binding shrink-to-fit request.
-\end{note}
+otherwise.
+Reallocation happens at this point if and only if
+the current capacity is less than the argument of \tcode{reserve()}.
 
 \pnum
 \throws