commit 0789bb7c9b07c1dbcf0fb937e3f9f96165c86031
Author: Daniel Swanson <popcorn.tomato.dude@gmail.com>
Date:   Tue Jul 27 09:45:23 2021 -0500

    string_view for old compilers

diff --git a/configure.ac b/configure.ac
index 05fce75..96baab2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -46,7 +46,7 @@ AC_CHECK_LIB(xml2, xmlReaderForFile)
 
 # Checks for header files.
 AC_HEADER_STDC
-AC_CHECK_HEADERS([stdlib.h string.h unistd.h stddef.h])
+AC_CHECK_HEADERS([stdlib.h string.h unistd.h stddef.h string_view])
 AC_CHECK_HEADER([utf8.h], [], [AC_MSG_ERROR([You don't have utfcpp installed.])])
 
 # Checks for typedefs, structures, and compiler characteristics.
diff --git a/lttoolbox/string_view.h b/lttoolbox/string_view.h
new file mode 100644
index 0000000..f5bf267
--- /dev/null
+++ b/lttoolbox/string_view.h
@@ -0,0 +1,40 @@
+/*
+* Copyright (C) 2021 Apertium
+*
+* This program 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 2 of the License, or
+* (at your option) any later version.
+*
+* This program 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 program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+#ifndef LT_STRING_VIEW_HPP__
+#define LT_STRING_VIEW_HPP__
+
+#ifdef HAVE_STRING_VIEW
+	#include <string_view>
+#else
+	#include <string>
+	#include <experimental/string_view>
+
+	namespace std {
+		using string_view = ::std::experimental::string_view;
+		template<typename T>
+		using basic_string_view = ::std::experimental::basic_string_view<T>;
+
+		inline ::std::string& operator+=(::std::string& str, ::std::string_view sv) {
+			str.append(sv.begin(), sv.end());
+			return str;
+		}
+	}
+#endif
+
+#endif
diff --git a/lttoolbox/ustring.h b/lttoolbox/ustring.h
index 3642cbe..5ffa878 100644
--- a/lttoolbox/ustring.h
+++ b/lttoolbox/ustring.h
@@ -24,7 +24,7 @@
 #include <vector>
 #include <cstdint>
 #include <iomanip>
-#include <string_view>
+#include <lttoolbox/string_view.h>
 
 typedef std::basic_string<UChar> UString;
 typedef std::basic_string_view<UChar> UString_view;