parametrize StringView

dbms/include/DB/Common/StringView.h

@@ -5,33 +5,46 @@
 #include <string>
 
 /// A lightweight non-owning read-only view into a subsequence of a string.
-class StringView
+template <
+	typename TChar,
+	typename TTraits = std::char_traits<TChar>
+>
+class StringViewImpl
 {
 public:
 	using size_type = size_t;
+	using traits_type = TTraits;
+	using value_type = typename TTraits::char_type;
 
 	static constexpr size_type npos = size_type(-1);
 
 public:
-	inline StringView() noexcept
+	inline StringViewImpl() noexcept
 		: str(nullptr)
 		, len(0)
 	{
 	}
 
-	constexpr inline StringView(const char* data_, size_t len_) noexcept
+	constexpr inline StringViewImpl(const TChar* data_, size_t len_) noexcept
 		: str(data_)
 		, len(len_)
 	{
 	}
 
-	inline StringView(const std::string& str) noexcept
+	inline StringViewImpl(const std::basic_string<TChar>& str) noexcept
 		: str(str.data())
 		, len(str.size())
 	{
 	}
 
-	inline const char* data() const noexcept
+	inline TChar at(size_type pos) const
+	{
+		if (pos >= len)
+			throw std::out_of_range("pos must be less than len");
+		return str[pos];
+	}
+
+	inline const TChar* data() const noexcept
 	{
 		return str;
 	}
@@ -58,14 +71,14 @@ public:
 	 * If the requested substring extends past the end of the string,
 	 * or if count == npos, the returned substring is [pos, size()).
 	 */
-	StringView substr(size_type pos, size_type count = npos) const
+	StringViewImpl substr(size_type pos, size_type count = npos) const
 	{
 		if (pos >= len)
 			throw std::out_of_range("pos must be less than len");
 		if (pos + count >= len || count == npos)
-			return StringView(str + pos, len - pos);
+			return StringViewImpl(str + pos, len - pos);
 		else
-			return StringView(str + pos, count);
+			return StringViewImpl(str + pos, count);
 	}
 
 public:
@@ -74,15 +87,39 @@ public:
 		return !empty();
 	}
 
+	inline TChar operator [] (size_type pos) const noexcept
+	{
+		return str[pos];
+	}
+
+	inline bool operator < (const StringViewImpl& other) const noexcept
+	{
+		if (len < other.len)
+			return true;
+		if (len > other.len)
+			return false;
+		return TTraits::compare(str, other.str, len) < 0;
+	}
+
+	inline bool operator == (const StringViewImpl& other) const noexcept
+	{
+		if (len == other.len)
+			return TTraits::compare(str, other.str, len) == 0;
+		return false;
+	}
+
 private:
-	const char* str;
+	const TChar* str;
 	size_t len;
 };
 
 
 /// It creates StringView from literal constant at compile time.
-template <size_t size>
-constexpr inline StringView MakeStringView(const char (&str)[size])
+template <typename TChar, size_t size>
+constexpr inline StringViewImpl<TChar> MakeStringView(const TChar (&str)[size])
 {
-    return StringView(str, size - 1);
+    return StringViewImpl<TChar>(str, size - 1);
 }
+
+
+using StringView = StringViewImpl<char>;