Implement LWG 2758.

	* include/bits/basic_string.h
	(append(__sv_type, size_type, size_type)): Turn into a template,
	change parameter type, constrain, add a conversion to __sv_type
	from the dependent parameter type.
	(assign(__sv_type, size_type, size_type)): Likewise.
	(insert(size_type, __sv_type, size_type, size_type)): Likewise.
	(replace(size_type, size_type, __sv_type, size_type, size_type)):
	Likewise.
	(compare(size_type, size_type,__sv_type, size_type, size_type)):
	Likewise.
	* testsuite/21_strings/basic_string/lwg2758.cc: New.

From-SVN: r239370

libstdc++-v3/ChangeLog

+2016-08-11  Ville Voutilainen  <ville.voutilainen@gmail.com>
+
+	Implement LWG 2758.
+	* include/bits/basic_string.h
+	(append(__sv_type, size_type, size_type)): Turn into a template,
+	change parameter type, constrain, add a conversion to __sv_type
+	from the dependent parameter type.
+	(assign(__sv_type, size_type, size_type)): Likewise.
+	(insert(size_type, __sv_type, size_type, size_type)): Likewise.
+	(replace(size_type, size_type, __sv_type, size_type, size_type)):
+	Likewise.
+	(compare(size_type, size_type,__sv_type, size_type, size_type)):
+	Likewise.
+	* testsuite/21_strings/basic_string/lwg2758.cc: New.
+
 2016-08-06  Jonathan Wakely  <jwakely@redhat.com>
 
 	* doc/xml/manual/status_cxx2017.xml: Update status table.

libstdc++-v3/include/bits/basic_string.h

@@ -1227,9 +1227,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  @param __n   The number of characters to append from the string_view.
        *  @return  Reference to this string.
        */
-      basic_string& append(__sv_type __sv,
+      template <typename _Tp,
+		enable_if_t<is_convertible_v<const _Tp&, __sv_type>,
+			    bool> = true>
+      basic_string& append(const _Tp& __svt,
 			   size_type __pos, size_type __n = npos)
       {
+	__sv_type __sv = __svt;
 	return _M_append(__sv.data()
 			 + __sv._M_check(__pos, "basic_string::append"),
 			 __sv._M_limit(__pos, __n));
@@ -1392,10 +1396,14 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  @param __n  The number of characters to assign.
        *  @return  Reference to this string.
        */
+      template <typename _Tp,
+		enable_if_t<is_convertible_v<const _Tp&, __sv_type>,
+			    bool> = true>
       basic_string&
-      assign(__sv_type __sv,
+      assign(const _Tp& __svt,
 	     size_type __pos, size_type __n = npos)
       {
+	__sv_type __sv = __svt;
 	return _M_replace(size_type(0), this->size(), __sv.data()
 			  + __sv._M_check(__pos, "basic_string::assign"),
 			  __sv._M_limit(__pos, __n));
@@ -1652,9 +1660,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  @param __n    The number of characters to insert.
        *  @return  Reference to this string.
       */
-      basic_string& insert(size_type __pos1, __sv_type __sv,
+      template <typename _Tp,
+		enable_if_t<is_convertible_v<const _Tp&, __sv_type>,
+			    bool> = true>
+      basic_string& insert(size_type __pos1, const _Tp& __svt,
 			   size_type __pos2, size_type __n = npos)
       {
+	__sv_type __sv = __svt;
 	return this->replace(__pos1, size_type(0), __sv.data()
 			     + __sv._M_check(__pos2, "basic_string::insert"),
 			     __sv._M_limit(__pos2, __n));
@@ -2071,10 +2083,14 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  @param __n2    The number of characters to insert.
        *  @return  Reference to this string.
       */
+      template <typename _Tp,
+		enable_if_t<is_convertible_v<const _Tp&, __sv_type>,
+			    bool> = true>
       basic_string& replace(size_type __pos1, size_type __n1,
-			    __sv_type __sv,
+			    const _Tp& __svt,
 			    size_type __pos2, size_type __n2 = npos)
       {
+	__sv_type __sv = __svt;
 	return this->replace(__pos1, __n1, __sv.data()
 			     + __sv._M_check(__pos2, "basic_string::replace"),
 			     __sv._M_limit(__pos2, __n2));
@@ -2720,10 +2736,14 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  @param __n2  The number of characters to compare.
        *  @return  Integer < 0, 0, or > 0.
        */
+      template <typename _Tp,
+		enable_if_t<is_convertible_v<const _Tp&, __sv_type>,
+			    bool> = true>
       int compare(size_type __pos1, size_type __n1,
-		  __sv_type __sv,
+		  const _Tp& __svt,
 		  size_type __pos2, size_type __n2 = npos) const
       {
+	__sv_type __sv = __svt;
 	return __sv_type(*this)
 	  .substr(__pos1, __n1).compare(__sv.substr(__pos2, __n2));
       }

libstdc++-v3/testsuite/21_strings/basic_string/lwg2758.cc

+// { dg-options "-std=gnu++17" }
+// { dg-do compile }
+
+// Copyright (C) 2016 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <string>
+
+struct CustomString
+{
+  std::string data = "foo";
+  std::string_view data_view = data;
+  operator std::string_view() const {return data_view;}
+};
+
+int main()
+{
+    std::string x;
+    CustomString cs;
+    x.append("foo", 0, 3);
+    x.append(cs, 0, 3);
+    x.assign("foo", 0, 3);
+    x.assign(cs, 0, 3);
+    x.insert(0, "foo", 0, 3);
+    x.insert(0, cs, 0, 3);
+    x = "bar";
+    x.replace(0, 3, "foo", 0, 3);
+    x.replace(0, 3, cs, 0, 3);
+    x = "bar";
+    x.compare(0, 3, "foo", 0, 3);
+    x.compare(0, 3, cs, 0, 3);
+}