Default Arguments

When you want to register a method or a constructor which contains default arguments, you have to provide them RTTR explicitly. The reason for this is, default arguments are not part of the function signature. Nevertheless, RTTR provides a mechanism to register functions with default arguments.

Please take a look at following example:

using namespace rttr;

void my_function(int a, bool b, const std::string& text, const int* ptr);

RTTR_REGISTRATION
{
    registration::method("my_function", &my_function)   
    (
        default_arguments(true, std::string("default text"), nullptr)
    );
}

The default arguments has to be provided via the function: default_arguments(). Place the call in the () operator of the returned bind object.

The function has following synopsis:

template<typename...TArgs>
detail::default_args<TArgs...> default_arguments(TArgs&&...args)

The values will be copied internally and will be provided during invoke of the method or constructor, when the corresponding argument is missing:

int main()
{
    using namespace rttr;
    method meth = type::get_global_method("my_function");
    // the default values: 'true', 'std::string("default text"'), 'nullptr' will be forwarded by RTTR automatically
    variant var = meth.invoke(instance(), 23);
    std::cout << var.is_valid(); // prints 'true'

    // the default value: 'nullptr' will be forwarded by RTTR automatically
    var = meth.invoke(instance(), 23, true, std::string("text"));
    std::cout << var.is_valid(); // prints 'true'
}

Remarks

The given arguments must match the signature from the starting position to the right most argument.

The following snippet will not compile and will raise a static_assert:

using namespace rttr;

void my_function(int a, bool b, const std::string& text, const int* ptr);

RTTR_REGISTRATION
{
    registration::method("my_function", &my_function)   
    (
        default_arguments(std::string("default text")) // default value for "ptr" not given
    );
}

Every method and constructor can have default arguments.

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