C++ MetaClass CookBook

meta_class_cookbook.cpp

// API Documentation was created based on the presentation of Herb Sutter on CppCon 2018:
//   https://www.youtube.com/watch?v=80BZxujhY38
// and the original propsal:
//   http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2018/p0707r3.pdf
// and test from the implementation repo
//   https://github.com/asutton/clang/tree/095a810d0514ccc9b3ea66c546a2adc7384449ca/test/CXX/meta

// Create a meta class
template <typename T>
constexpr void meta_class(T source){
    // Do something with the source class
}

// Apply the meta class to a class
class(meta_class) MyClass {
    
};

//
// Reflections
//

// Member function of class source
source.functions();
source.member_functions();

// Get the return type of the member function
function.return_type();

// Member variables of class source
source.variables();
source.member_variables();

// Get the type of a member variable
variable.type();

// Name of member function
function.name();

// Compare member function name to a string
if(std::strcmp(function.name(), "foo")==0){
    // Do something on the function
}

// Iterate over a list of meta information
for... (auto variable: source.variables){
    // Do something on variable
}

// Check for public or private
variable.is_public();
variable.is_private();
function.is_public();
function.is_private();

// Check for constructor / destructor
function.is_constructor();
function.is_destructor();

//
// Generation
//

// Generate a public member function
__generate __fragment struct {
   int bar(int a){return a;}
};

// Generate a private member function
__generate __fragment class {
   int bar(int a){return a;}
};

// Generae a public member variable
__generate __fragment struct {
   int b;
}

// Generae a private member variable
__generate __fragment class {
   int b;
}

// Make member variable private
variable.make_private();

// Make member variable public
variable.make_public();

// Make member function private
function.make_private();

// Make member function public
function.make_public();

// Make member function pure virtual
function.make_pure_virtual();

// Generate member function with custom name and type
__generate __fragment struct {
    typename(variable) idexpr("get_", variable)() const {
        return idexpr(variable);
    }
};
 

//
// Compiler object
//

// Print generate code of Test class
constexpr {compiler.debug($Test);}

// Assert on generated code
compiler.require(!source.variables().empty(), "Need to have member variables");