Classes

For registering classes in RTTR you use a class called registration::class_<T>. Its name is supposed to resemble the C++ keyword, to make it look more intuitive. It has member functions for register constructors, properties, methods and enums. These functions have the same interface and work in the same way like register the global symbols. Every call to these member functions, will return bind object, in order to chain more registration calls.

Let's start with a simple example. Consider the following C++ class:

#include <rttr/type>
// test class.h
struct test_class
{
test_class(int value) : m_value(value) {}
void print_value() const { std::cout << m_value; }
int m_value;
};

The registration process is now done at global scope in the cpp file.

// test_class.cpp
#include <rttr/registration>
{
using namespace rttr;
.method("print_value", &test_class::print_value)
.property("value", &test_class::m_value);
}

This will register the class test_class with a constructor that takes an integer as argument, a member function with the name print_value and a property called value.

The property name has to be unique for this class type, but derived classes can register another property with the same name again. Member functions can be overloaded, so a method can be registered with an already existing name multiple times. However when there exist a method with the same name and signature, then this function will not be registered and discarded.

Overloaded member functions

In order to register a overloaded member function, you have to disambiguate the member function pointer you pass to method. Therefore a helper function can be used: select_overload<T>(T (ClassType::*func))

Here's an example illustrating this:

struct Foo
{
void f() {}
void f(int) {}
void f(int) const {}
};
{
using namespace rttr;
.method("f", select_overload<void(void)>(&Foo::f))
.method("f", select_overload<void(int)>(&Foo::f))
.method("f", select_const(&Foo::f)); // register a overloaded const method
}

The last function is a overloaded const function, use therefore the select_const() function.

Register constructor

RTTR allows your to register constructors for classes. Because C++ doesn't allow to retrieve the member function pointer of a constructor you have to explicit specify all data types of a constructor.

Consider following class with three constructors:

struct Foo
{
Foo();
Foo(int, double);
Foo(const std::string&);
static Foo* create();
};

For registering three Foo constructors you now have to specify every parameter as template parameter in the member function constructor(). As second option, it is possible to register a static function as constructor. In order to do this, just forward the function pointer.

{
using namespace rttr;
.constructor<int,double>()
.constructor(&Foo::create);
}

When a constructor is registered a destructor is registered automatically. The used default policy for creating an instance is policy::ctor::as_object.

Register class properties

Register a public property can be easily done, consider following class:

struct Foo
{
int value;
};

This class is registered like this:

With the property() member function you will register the member variable Foo::value with read and write access.

Read Only Properties

When you want a register a property with read-only access, then this is also possible with property_readonly() member function.

{
using namespace rttr;
.property_readonly("value", &Foo::value);
}

Private Properties

When you have a class and the property is declared in private scope, then you can still register this property when you insert the macro: RTTR_REGISTRATION_FRIEND inside the class.

class Foo
{
private:
int value;
};

This will make this class a friend to the registration system.

Getter Setter For Properties

You can also register getter and setter functions and make them look as if they were a public data member. Consider the following class:

class Foo
{
public:
void set_value(int x) { m_value = x; }
int get_value() const { return m_value; }
private:
int m_value;
};

This is the registration code:

{
using namespace rttr;
.property("value", &Foo::get_value, &Foo::set_value);
}

This way, accessing the property will now call these functions, instead the property directly. Remark that the getter function needs the be const.

The following sub sections will now show how to retrieve these informations for creating, invoking and setting properties of an instance of this class.

Access Level Of Class Members

With RTTR it is also possible to specify on of the three access modifiers during the registration.

using namespace rttr;
struct Foo
{
public:
Foo() {}
protected:
void func() {}
private:
int value;
};
{
.constructor<>(registration::public_access) // not necessary, because that is the default
.method("func", &Foo::func, registration::protected_access)
}

The access level has to be specified as last argument in the corresponding class_ registration function. Use therefore one of the three static member variables in the registration class. This information can be retrieved at runtime for properties, methods or constructors. via the function get_access_level(), which will return a enum value of type access_levels.

Create/destroy of classes

There are two options for creating/destroying a class.

  1. use just the type interface or
  2. retrieve a constructor and destructor object from the type class.
int main()
{
using namespace rttr;
// option 1
type class_type = type::get_by_name("test_class");
if (class_type)
{
variant obj = class_type.create({23});
if (obj.get_type().is_pointer())
class_type.destroy(obj);
}
// option 2
if (class_type)
{
constructor ctor = class_type.get_constructor({type::get<int>()});
variant obj = ctor.invoke(23);
if (obj.get_type().is_pointer())
{
destructor dtor = class_type.get_destructor();
dtor.invoke(obj);
}
}
}

The objects which are constructed are created on the heap and stored as pointer in the variant object.

Invoke member functions

Invoking a member function works in the same way like invoking global function. The only difference is, that you have to provide the instance of the class.

int main()
{
using namespace rttr;
test_class obj(42);
type class_type = type::get_by_name("test_class");
// option 1
class_type.invoke("print_value", obj, {}); // print 42
// option 2
method print_meth = class_type.get_method("print_value");
print_meth.invoke(obj); // prints "42"
}

The invoke function also except to use variants. So when you create the object via the type constructor you can use the returned variant to invoke a method:

int main()
{
using namespace rttr;
variant obj_var = type::get_by_name("test_class").create({42});
type::get_by_name("test_class").invoke("print_value", obj_var, {}); // print 42
}

It is possible to invoke a method, when the instance is wrapped inside a wrapper class, for example std::shared_ptr<T>.

int main()
{
std::shared_ptr<test_class> obj = std::make_shared<test_class>(23);
method meth = type::get_by_name("test_class").get_method("print_value");
method.invoke(obj); // successful invoke
method.invoke(obj.get()); // successful invoke
method.invoke(*obj.get()); // successful invoke
variant var = obj;
// or use the variant
method.invoke(var); // successful invoke
return 0;
}

When you want to use RTTR with a custom wrapper type, you have provide a specialization of the class template wrapper_mapper<T>.

Set/Get property of a class

Properties can be also set and get in two steps:

int main()
{
using namespace rttr;
test_class obj(0);
type class_type = type::get_by_name("test_class");
// option 1
bool success = class_type.set_property_value("value", obj, 50);
std::cout << obj.m_value; // prints "50"
// option 2
property prop = class_type.get_property("value");
success = prop.set_value(obj, 24);
std::cout << obj.m_value; // prints "24"
}

In difference to the global properties, a valid type object and an instance (object) of the class is now needed to set and get the value. It doesn't matter in what hierarchy level the object is or if its a pointer, an object on the stack or wrapped inside a variant. RTTR will try to cast the given object to the class type where the property was registered to.