Merge 2024-03 LWG Motion 11

P2591R5 Concatenation of strings and string views

Author: tkoeppe

source/strings.tex

@@ -1836,6 +1836,22 @@
     constexpr basic_string<charT, traits, Allocator>
       operator+(basic_string<charT, traits, Allocator>&& lhs,
                 charT rhs);
+  template<class charT, class traits, class Allocator>
+    constexpr basic_string<charT, traits, Allocator>
+      operator+(const basic_string<charT, traits, Allocator>& lhs,
+                type_identity_t<basic_string_view<charT, traits>> rhs);
+  template<class charT, class traits, class Allocator>
+    constexpr basic_string<charT, traits, Allocator>
+      operator+(basic_string<charT, traits, Allocator>&& lhs,
+                type_identity_t<basic_string_view<charT, traits>> rhs);
+  template<class charT, class traits, class Allocator>
+    constexpr basic_string<charT, traits, Allocator>
+      operator+(type_identity_t<basic_string_view<charT, traits>> lhs,
+                const basic_string<charT, traits, Allocator>& rhs);
+  template<class charT, class traits, class Allocator>
+    constexpr basic_string<charT, traits, Allocator>
+      operator+(type_identity_t<basic_string_view<charT, traits>> lhs,
+                basic_string<charT, traits, Allocator>&& rhs);
 
   template<class charT, class traits, class Allocator>
     constexpr bool
@@ -4851,6 +4867,85 @@
 \end{codeblock}
 \end{itemdescr}
 
+\indexlibrarymember{operator+}{basic_string}%
+\begin{itemdecl}
+template<class charT, class traits, class Allocator>
+  constexpr basic_string<charT, traits, Allocator>
+    operator+(const basic_string<charT, traits, Allocator>& lhs,
+              type_identity_t<basic_string_view<charT, traits>> rhs);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+Equivalent to:
+\begin{codeblock}
+basic_string<charT, traits, Allocator> r = lhs;
+r.append(rhs);
+return r;
+\end{codeblock}
+\end{itemdescr}
+
+\indexlibrarymember{operator+}{basic_string}%
+\begin{itemdecl}
+template<class charT, class traits, class Allocator>
+  constexpr basic_string<charT, traits, Allocator>
+    operator+(basic_string<charT, traits, Allocator>&& lhs,
+              type_identity_t<basic_string_view<charT, traits>> rhs);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+Equivalent to:
+\begin{codeblock}
+lhs.append(rhs);
+return std::move(lhs);
+\end{codeblock}
+\end{itemdescr}
+
+\indexlibrarymember{operator+}{basic_string}%
+\begin{itemdecl}
+template<class charT, class traits, class Allocator>
+  constexpr basic_string<charT, traits, Allocator>
+    operator+(type_identity_t<basic_string_view<charT, traits>> lhs,
+              const basic_string<charT, traits, Allocator>& rhs);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+Equivalent to:
+\begin{codeblock}
+basic_string<charT, traits, Allocator> r = rhs;
+r.insert(0, lhs);
+return r;
+\end{codeblock}
+\end{itemdescr}
+
+\indexlibrarymember{operator+}{basic_string}%
+\begin{itemdecl}
+template<class charT, class traits, class Allocator>
+  constexpr basic_string<charT, traits, Allocator>
+    operator+(type_identity_t<basic_string_view<charT, traits>> lhs,
+              basic_string<charT, traits, Allocator>&& rhs);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+Equivalent to:
+\begin{codeblock}
+rhs.insert(0, lhs);
+return std::move(rhs);
+\end{codeblock}
+\end{itemdescr}
+
+\pnum
+\begin{note}
+Using a specialization of \tcode{type_identity_t} as a parameter type ensures
+that an object of type \tcode{basic_string<charT, traits, Allocator>}
+can be concatenated with an object of a type \tcode{T}
+having an implicit conversion to
+\tcode{basic_string_view<charT, traits>}\iref{over.match.oper}.
+\end{note}
+
 \rSec3[string.cmp]{Non-member comparison operator functions}
 \begin{itemdecl}
 template<class charT, class traits, class Allocator>

source/support.tex

@@ -779,7 +779,7 @@
 #define @\defnlibxname{cpp_lib_string_contains}@                   202011L // also in \libheader{string}, \libheader{string_view}
 #define @\defnlibxname{cpp_lib_string_resize_and_overwrite}@       202110L // also in \libheader{string}
 #define @\defnlibxname{cpp_lib_string_udls}@                       201304L // also in \libheader{string}
-#define @\defnlibxname{cpp_lib_string_view}@                       201803L // also in \libheader{string}, \libheader{string_view}
+#define @\defnlibxname{cpp_lib_string_view}@                       202403L // also in \libheader{string}, \libheader{string_view}
 #define @\defnlibxname{cpp_lib_submdspan}@                         202306L // also in \libheader{mdspan}
 #define @\defnlibxname{cpp_lib_syncbuf}@                           201803L // also in \libheader{syncstream}
 #define @\defnlibxname{cpp_lib_text_encoding}@                     202306L // also in \libheader{text_encoding}