error in making the file: expected primary-expression before ')' token - c++

Question

I have a struct defined as:
template<typename T>
struct unique_owned_item_filter: public std::unary_function<T,bool> {
unique_owned_item_filter(){}
bool operator()(const T& item)const {
return !item->shared() || item->owner() == MPI::COMM_WORLD.Get_rank();
}
typedef T item_type;
};
and I want to use this structure in a function like this
void read_nodes(std::ifstream& infile, mesh_type& mesh, const std::list<int>&my_nodes)
{
typedef typename mesh_type::node_t nd_t;
..... follows some code .....
create_double_nodes(mesh,unique_owned_item_filter<nd_t>);
}
where the function create_double_nodes is defined as
template<typename mesh_type, typename rule_type >
void create_double_nodes(mesh_type& mesh,rule_type& rule){
.... follows some code ....
}
When I pass to create_double_nodes the argument unique_owned_item_filter I insert
its dependence on the template parameter nd_t, that, in my case, is the mesh node
of type mesh_type::node_t.
When I compile the whole, I get the error expected primary-expression before ')' token at the declaration of create_double_nodes(mesh,unique_owned_item_filter<nd_t>);.
It seems to me that the template argument is right.
Can somebody help me?
The problem in the definition of the create_double_nodes disappeared, but now the problem appeared inside the body of the function itself.
template<typename mesh_type, typename rule_type >
void create_double_nodes(mesh_type& mesh, const rule_type& rule){
typename mesh_type::nd_set_t::const_iterator it_first( mesh.nodes().begin());
while(it_first!=mesh.nodes().end()){
if(rule(*it_first))
....follows code ....
it_first++
}
when i apply the rule to the const iterator it does not accept it. The compilation gives the following error:
no match for call to '(const GALES::unique_owned_item_filter, 5, GALES::base_5_dofs> >) (GALES::fem_node, 5, GALES::base_5_dofs>* const&)'
with candidates
bool GALES::unique_owned_item_filter<T>::operator()(const T&) const [with T = GALES::fem_node<GALES::geometric_node<2>, 5, GALES::base_5_dofs>]
where
GALES::fem_node<GALES::geometric_node<2>, 5, GALES::base_5_dofs>
is the complete type of node of the mesh.
I cannot understand why the rule applied to a constant iterator is not accepted. If you need more details I will try to explain it better.
Thank you very much again.

Answer 1

unique_owned_item_filter<nd_t> is a type, but you're using it as a function argument, where a value is required. You probably wanted to create an object of this type instead:
create_double_nodes(mesh, unique_owned_item_filter<nd_t>());
// ^^ parens here!
This will not work as-is, though, because your function template create_double_nodes takes the second parameter by non-const reference, and such cannot bind to a temporary (such as the one created in my example above).
You have two solutions: either change create_double_nodes to take its parameter by const-reference, or create a named object for the argument:
unique_owned_item_filter<nd_t> filter;
create_double_nodes(mesh, filter);

Answer 2

1.Make it an object:
create_double_nodes(mesh,unique_owned_item_filter<nd_t>());
^^
2.Pass by const reference or value:
void create_double_nodes(mesh_type& mesh, const rule_type& rule){
^^^^^