Methods - 0.9.6 |RTTR

As already mentioned to register global methods to RTTR use the function registration::method(). It has following synopsis:

template<typename F>
  • name is the name of the function
  • F is the function pointer or std::function your want to register

For example when you want to register the byte string to integer conversion function: int atoi (const char * str);

Do it in the following way:

#include <rttr/registration>
#include <cstdlib>
using namespace rttr;
registration::method("atoi", &atoi);

Overloaded Methods

When you want to register a function which is overloaded (same name, different signature), you should use the helper function: select_overload<T>(T*)

This will avoid the hassle with the function pointer signature. For example the two functions: float sin (float x); and double sin (double x); can be registered like following:

#include <rttr/registration>
#include <cmath>
using namespace rttr;
registration::method("sin", select_overload<float(float)>(&sin))
.method("sin", select_overload<double(double)>(&sin));

It is possible the chain multiple registration calls, because of the temporary returned bind object.

The select_overload function cannot be used with MSVC x86 compiler, because of the different calling convention for global- and member-functions. See here for a workaround.

Invoke of methods

Invoking a method with RTTR can be done in two ways:

The first option needs less typing, but it is slower when you need to invoke the function several times. For the second option you need more code to write, but it invokes the method faster.

The following example demonstrates the possibilities to invoke a method:

using namespace rttr;
int main()
// let asume we have registered the pow function: double pow( double base, double exp );
// option 1
variant return_value = type::invoke("pow", {9.0, 2.0});
if (return_value.is_valid() && return_value.is_type<double>())
std::cout << return_value.get_value<double>() << std::endl; // 81
// option 2
if (meth) // check if the function was found
return_value = meth.invoke({}, 9.0, 3.0); // invoke with empty instance
if (return_value.is_valid() && return_value.is_type<double>())
std::cout << return_value.get_value<double>() << std::endl; // 729

The type::invoke() function will internally try to find a function based on the given name and the given types of the arguments. So finding the correct function when overloaded function are registered is automatically done. Notice that you have to provide the arguments as a vector pack. Therefore an initializer list is quite handy to reduce typing. The argument must match 100%, there is at the moment no conversion done. That means, when an integer argument is needed and you forward a double value the function will not be called. The arguments will not be copied, instead they will be wrapped in an internal class and forwarded to the underlying function pointer. This class is called argument do not create this class on your own. The class will implicit wrap your argument value.

The return value of type::invoke() is a variant object. It indicates whether the function was called or not. RTTR does not use the exception mechanism of C++, therefore you have to check the return values when you are interested in a successful call. The rttr::variant object is valid when it was successfully called. When the function has a return value, then this value is also contained in the variant object.

When you prefer to hold a handle to the function use the getter type::get_global_method() to retrieve a method object. This has the advantage that you do not need to search for the function every time you want to invoke it. Additionally this class provides functions to invoke a function without the need to create a vector of arguments. The method object is lightweight and can be simply copied around different locations. The object stays valid till end of the main() function.