Fix build for modern C++17 and Clang 17

Modernize the project to build with contemporary toolchains:

- Upgrade C++ standard from C++11 to C++17
- Update CMake minimum version to 3.16
- Fix logger comparator const-correctness for modern libc++
- Resolve namespace/class name ambiguity using inline variables
- Use typedef alias to disambiguate out-of-line member definitions

The dotenv class name matches its namespace, which causes parsing
issues in modern C++. Fixed by using C++17 inline variables for
static members and a typedef alias in the implementation.

Author: renecannao

CMakeLists.txt

@@ -1,8 +1,8 @@
 #----------------------- PROJECT CONFIGURATION --------------------------------
-cmake_minimum_required(VERSION 3.10)
+cmake_minimum_required(VERSION 3.16)
 project(cpp-dotenv VERSION 1.0.0)
 
-set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 if ("${CMAKE_BUILD_TYPE}" STREQUAL "")

common/libs/antlr4-cpp-runtime/CMakeLists.txt

@@ -1,7 +1,7 @@
-cmake_minimum_required(VERSION 3.0.2)
+cmake_minimum_required(VERSION 3.10)
 project(antlr4-cpp-runtime VERSION 4.8)
 
-set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 if ("${CMAKE_BUILD_TYPE}" STREQUAL "")

include/dotenv.h

@@ -15,7 +15,7 @@ namespace dotenv
 
     public:
 
-        dotenv& load_dotenv(const std::string& dotenv_path = env_filename,
+        dotenv& load_dotenv(const std::string& dotenv_path = ".env",
                             const bool overwrite = false,
                             const bool interpolate = true);
 
@@ -28,7 +28,7 @@ namespace dotenv
         void operator=(const dotenv&) = delete;
 
         static dotenv& instance();
-    
+
     private:
 
         dotenv() = default;
@@ -42,4 +42,8 @@ namespace dotenv
 
 
     extern dotenv& env;
+
+    // Inline variables defined after class is complete (C++17)
+    inline const std::string dotenv::env_filename = ".env";
+    inline dotenv dotenv::_instance;
 }

src/common/logger.cpp

@@ -21,7 +21,7 @@ bool logger::position::operator<(const position& p) const
 }
 
 
-bool logger::position::less::operator()(const position& p1, const position& p2)
+bool logger::position::less::operator()(const position& p1, const position& p2) const
 {
     return p1 < p2;
 }

src/common/logger.h

@@ -31,7 +31,7 @@ namespace dotenv
 
             struct less
             {
-                bool operator()(const position& p1, const position& p2);
+                bool operator()(const position& p1, const position& p2) const;
             };
 
         public:

src/dotenv.cpp

@@ -8,10 +8,14 @@
 
 
 using namespace std;
-using namespace dotenv;
 
 
-dotenv::dotenv& dotenv::dotenv::load_dotenv(const string& dotenv_path, const bool overwrite, const bool interpolate)
+// Typedef to work around the fact that class name matches namespace name
+// This is a known C++ limitation when defining out-of-line members
+typedef class ::dotenv::dotenv Dotenv_Type;
+
+
+Dotenv_Type& ::dotenv::dotenv::load_dotenv(const string& dotenv_path, const bool overwrite, const bool interpolate)
 {
     ifstream env_file;
     env_file.open(dotenv_path);
@@ -27,19 +31,17 @@ dotenv::dotenv& dotenv::dotenv::load_dotenv(const string& dotenv_path, const boo
 }
 
 
-const dotenv::dotenv::value_type dotenv::dotenv::operator[](const key_type& k) const
+auto ::dotenv::dotenv::operator[](const key_type& k) const -> const string
 {
     return getenv(k).second;
 }
 
 
-dotenv::dotenv& dotenv::dotenv::instance()
+Dotenv_Type& ::dotenv::dotenv::instance()
 {
     return _instance;
 }
 
 
-const string dotenv::dotenv::env_filename = ".env";
-dotenv::dotenv dotenv::dotenv::_instance;
-
-dotenv::dotenv& dotenv::env = dotenv::instance();
+// Static members are now inline in the header (C++17)
+::dotenv::dotenv& ::dotenv::env = ::dotenv::dotenv::instance();