Update single header

Author: edisonhello

single_include/tabulate/tabulate.hpp

@@ -6147,6 +6147,7 @@ inline size_t get_sequence_length(const std::string &text, const std::string &lo
     return text.length();
 
 #if defined(_WIN32) || defined(_WIN64)
+  (void) locale; // unused parameter
   return (text.length() - std::count_if(text.begin(), text.end(),
                                         [](char c) -> bool { return (c & 0xC0) == 0x80; }));
 #elif defined(__unix__) || defined(__unix) || defined(__APPLE__)
@@ -7531,7 +7532,15 @@ SOFTWARE.
 #include <functional>
 #include <iostream>
 #include <memory>
+
+#if __cplusplus >= 201703L
 #include <optional>
+using std::optional;
+#else
+// #include <tabulate/optional_lite.hpp>
+using nonstd::optional;
+#endif
+
 #include <string>
 // #include <tabulate/cell.hpp>
 // #include <tabulate/column_format.hpp>
@@ -8610,17 +8619,17 @@ SOFTWARE.
 #include <variant>
 using std::get_if;
 using std::holds_alternative;
+using std::string_view;
 using std::variant;
 using std::visit;
-using std::string_view;
 #else
 // #include <tabulate/string_view_lite.hpp>
 // #include <tabulate/variant_lite.hpp>
 using nonstd::get_if;
 using nonstd::holds_alternative;
+using nonstd::string_view;
 using nonstd::variant;
 using nonstd::visit;
-using nonstd::string_view;
 #endif
 
 #include <utility>
@@ -8631,7 +8640,8 @@ class Table {
 public:
   Table() : table_(TableInternal::create()) {}
 
-  using Row_t = std::vector<variant<std::string, const char *, string_view, Table>>;
+  using Row_t =
+      std::vector<variant<std::string, const char *, string_view, Table>>;
 
   Table &add_row(const Row_t &cells) {
 
@@ -8656,7 +8666,7 @@ class Table {
         cell_strings[i] = *get_if<std::string>(&cell);
       } else if (holds_alternative<const char *>(cell)) {
         cell_strings[i] = *get_if<const char *>(&cell);
-      }  else if (holds_alternative<string_view>(cell)) {
+      } else if (holds_alternative<string_view>(cell)) {
         cell_strings[i] = std::string{*get_if<string_view>(&cell)};
       } else {
         auto table = *get_if<Table>(&cell);
@@ -8687,11 +8697,14 @@ class Table {
     return stream.str();
   }
 
+  size_t size() const { return table_->size(); }
+
   std::pair<size_t, size_t> shape() { return table_->shape(); }
 
   class RowIterator {
   public:
-    explicit RowIterator(std::vector<std::shared_ptr<Row>>::iterator ptr) : ptr(ptr) {}
+    explicit RowIterator(std::vector<std::shared_ptr<Row>>::iterator ptr)
+        : ptr(ptr) {}
 
     RowIterator operator++() {
       ++ptr;