// Code derived from Stroustrup's PPP2 book
// § 8.7 Namespaces
//  -and beginning on p 295

// clang-format off
namespace Graph_lib {

struct Color { /* ... */ };
struct Shape { /* ... */ };
struct Line : Shape { /* ... */ };
struct Function : Shape { /* ... */ }; 
struct Text : Shape { /* ... */ };

// ...

int gui_main() { /* ... */ return 0; }

}  // namespace Graph_lib

namespace TextLib {

class Text { /* ... */ };
class Glyph {  /* ... */ };
class Line {  /* ... */ };

// ...

}  // namespace TextLib
// clang-format on

int main() { return Graph_lib::gui_main(); }