Merge 2019-11 LWG Motion 12

P1391R4 Range constructor for std::string_view

Author: zygoloid

source/strings.tex

@@ -4020,6 +4020,8 @@
   constexpr basic_string_view& operator=(const basic_string_view&) noexcept = default;
   constexpr basic_string_view(const charT* str);
   constexpr basic_string_view(const charT* str, size_type len);
+  template<class It, class End>
+    constexpr basic_string_view(It begin, End end);
 
   // \ref{string.view.iterators}, iterator support
   constexpr const_iterator begin() const noexcept;
@@ -4106,6 +4108,10 @@
   const_pointer data_;          // \expos
   size_type size_;              // \expos
 };
+
+// \ref{string.view.deduct}, deduction guide
+template<class It, class End>
+  basic_string_view(It, End) -> basic_string_view<iter_value_t<It>>;
 \end{codeblock}
 
 \pnum
@@ -4174,6 +4180,36 @@
 and initializing \tcode{size_} with \tcode{len}.
 \end{itemdescr}
 
+\indexlibraryctor{basic_string_view}%
+\begin{itemdecl}
+template<class It, class End>
+  constexpr basic_string_view(It begin, End end);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\constraints
+\begin{itemize}
+\item \tcode{It} satisfies \libconcept{contiguous_iterator}.
+\item \tcode{End} satisfies \tcode{\libconcept{sized_sentinel_for}<It>}.
+\item \tcode{is_same_v<iter_value_t<It>, charT>} is \tcode{true}.
+\item \tcode{is_convertible_v<End, size_type>} is \tcode{false}.
+\end{itemize}
+
+\pnum
+\expects
+\begin{itemize}
+\item \range{begin}{end} is a valid range.
+\item \tcode{It} models \libconcept{contiguous_iterator}.
+\item \tcode{End} models \tcode{\libconcept{sized_sentinel_for}<It>}.
+\end{itemize}
+
+\pnum
+\effects
+Initializes \tcode{data_} with \tcode{to_address(begin)} and
+initializes \tcode{size_} with \tcode{end - begin}.
+\end{itemdescr}
+
 \rSec3[string.view.iterators]{Iterator support}
 
 \indexlibrarymember{const_iterator}{basic_string_view}%
@@ -4836,6 +4872,22 @@
 Otherwise, returns \tcode{npos}.
 \end{itemdescr}
 
+\rSec2[string.view.deduct]{Deduction guide}
+
+\begin{itemdecl}
+template<class It, class End>
+  basic_string_view(It, End) -> basic_string_view<iter_value_t<It>>;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\constraints
+\begin{itemize}
+\item \tcode{It} satisfies \libconcept{contiguous_iterator}.
+\item \tcode{End} satisfies \tcode{\libconcept{sized_sentinel_for}<It>}.
+\end{itemize}
+\end{itemdescr}
+
 \rSec2[string.view.comparison]{Non-member comparison functions}
 
 \pnum