implement the C++20 methods. makes nfc_string a boost::totally_ordered2 with StringView.

src/nfc.cc

@@ -766,7 +766,26 @@ UTF<CharT>::nfc_string& UTF<CharT>::nfc_string::operator+=(const UTF<CharT>::nfc
 	return *this;
 }
 
+template<class CharT>
+bool UTF<CharT>::nfc_string::starts_with(StringView sv) const noexcept
+{
+	return (s.size() >= sv.size())
+	 && (StringView{s.data(), sv.size()} == sv);
+}
 
+template<class CharT>
+bool UTF<CharT>::nfc_string::ends_with(StringView sv) const noexcept
+{
+	return (s.size() >= sv.size())
+	 && (StringView{s.data() + s.size() - sv.size(), sv.size()} == sv);
+}
+
+template<class CharT>
+typename
+UTF<CharT>::nfc_string UTF<CharT>::nfc_string::substr(std::size_t pos, std::size_t count) const
+{
+	return nfc_string{s.substr(pos,count)};
+}
 
 // convenience function to avoid ::strdup(pEp::toNFC<char>(text).c_str());
 // and unecessary temporary std::string etc.

src/nfc.hh

@@ -8,6 +8,7 @@
 #include <string>
 #include <stdexcept>
 #include <iosfwd>
+#include <boost/operators.hpp>
 #include <pEp/identity_list.h>
 
 namespace pEp {
@@ -82,7 +83,7 @@ public:
 	
 	/// class holding a NFC-conform Unicode string.
 	/// content is mostly read-only, because arbitrary modifications might destroy NFC conformacy.
-	class nfc_string
+	class nfc_string : public boost::totally_ordered2<nfc_string, std::basic_string_view<CharT>>
 	{
 	public:
 		typedef std::basic_string<CharT>      String;
@@ -195,10 +196,10 @@ public:
 		}
 		
 		/// stolen from C++20
-		bool starts_with(StringView s) const;
+		bool starts_with(StringView s) const noexcept;
 		
 		/// stolen from C++20
-		bool ends_with(StringView s) const;
+		bool ends_with(StringView s) const noexcept;
 		
 		/// delegates all 5 find() overloads to s
 		template<typename... Args>
@@ -210,8 +211,6 @@ public:
 		/// might throw illegal_utf, if a multi-char sequence is clipped.
 		nfc_string substr(std::size_t pos=0, std::size_t count=npos) const;
 		
-		
-		
 	private:
 		std::basic_string<CharT> s;
 		
@@ -249,10 +248,25 @@ inline
 typename
 UTF<CharT>::nfc_string operator+(const T& left, const typename UTF<CharT>::nfc_string& right)
 {
-	UTF<CharT> left_s{left};
+	typename UTF<CharT>::nfc_string left_s{left};
 	return left_s+=right;
 }
 
+template<class CharT>
+inline
+bool operator<(const typename UTF<CharT>::nfc_string& left, std::basic_string_view<CharT> right)
+{
+	return left<right;
+}
+
+template<class CharT>
+inline
+bool operator==(const typename UTF<CharT>::nfc_string& left, std::basic_string_view<CharT> right)
+{
+	return left==right;
+}
+
+
 /// convenient alias names:
 using UTF8 = UTF<char>;
 using UTF16 = UTF<char16_t>;