How to get element from std::tuple by type

Question

I have a set of classes A, B, C and I want to have access instances of them from generic code by type, f.e

template
newObject()
{
    retur         


        

Answer 1

A simple variadic mixin container does the trick:

template < typename T > struct type_tuple_value 
{ 
    T value; 
    type_tuple_value ( T&& arg ) : value(std::forward(arg)) {}
};

template < typename ...T > struct type_tuple : type_tuple_value...
{
    template < typename ...Args > type_tuple ( Args&&... args ) :
    type_tuple_value(std::forward(args))... {}
    template < typename U > U& get() { return type_tuple_value::value; }
    template < typename U > const U& get() const { return type_tuple_value::value; }
};

Example