no using global namespace

src/lox.cpp

@@ -7,7 +7,7 @@
 #include <string>
 #include <vector>
 
-using namespace std;
+using std::string, std::vector, std::ifstream, std::cin, std::cout;
 
 void print_tokens(vector<Token> *list);
 int run_file(string file);

src/parser.cpp

@@ -3,7 +3,7 @@
 #include <iostream>
 #include <memory>
 
-using namespace std;
+using std::string, std::to_string, std::vector;
 
 Expression::~Expression() = default;
 

src/scanner.cpp

@@ -7,7 +7,7 @@
 #include <string>
 #include <vector>
 
-using namespace std;
+using std::string, std::map, std::vector, std::cout;
 
 static const map<string, Token::Type> keywords = {
     {"and", Token::Type::AND},       {"class", Token::Type::CLASS},

src/tokens.cpp

@@ -1,6 +1,6 @@
 #include "tokens.hpp"
 
-using namespace std;
+using std::string;
 
 Token::Token(Token::Type _tokentype, string _lexeme, string _literal, int _line)
     : lexeme(_lexeme), literal(_literal), line(_line), tokentype(_tokentype) {}