Any Solution to Unpack a Vector to Function Arguments in C++?

Question

I am actually thinking of something similar to the \'*\' operator in python like this:

args = [1,2,4]
f(*args)

Is there a similar solution

Answer 1

Update to @Fernandes's answer.

Yes, there does be a way to remove the need to specifying num_args in template parameter. This is because num_args is determined by the function signature, not the vector. What should be checked at run-time is the size of the vector and the arity of the function.

See the following example.

#include 
#include 
#include 
#include 

namespace util {
template 
struct function_traits_defs {
  static constexpr size_t arity = sizeof...(Args);

  using result_type = ReturnType;

  template 
  struct arg {
    using type = typename std::tuple_element>::type;
  };
};

template 
struct function_traits_impl;

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits_impl
    : function_traits_defs {};

template 
struct function_traits
    : function_traits_impl {};

template 
struct function_traits
    : function_traits_impl {};

template 
struct indices {
  using next = indices;
};
template 
struct build_indices {
  using type = typename build_indices::type::next;
};
template <>
struct build_indices<0> {
  using type = indices<>;
};
template 
using BuildIndices = typename build_indices::type;

namespace details {
template ,
          typename ReturnT = typename Traits::result_type>
ReturnT do_call(FuncType& func,
                VecType& args,
           indices ) {
  assert(args.size() >= Traits::arity);
  return func(args[I]...);
}
}  // namespace details

template ,
          typename ReturnT = typename Traits::result_type>
ReturnT unpack_caller(FuncType& func,
                VecType& args) {
  return details::do_call(func, args, BuildIndices());
}
}  // namespace util

int func(int a, int b, int c) {
  return a + b + c;
}

int main() {
  std::vector args = {1, 2, 3};

  int j = util::unpack_caller(func, args);
  std::cout << j << std::endl;

  return 0;
}