Should this work?
I'm trying to specialize metafunction to a type that has a function pointer as one of its parameters. The code compiles just fine, but it just doesn't match the type.
#include <iostream>
#include <boost/mpl/bool.hpp>
#include <boost/mpl/identity.hpp>
template < typename CONT, typename NAME, typename TYPE, TYPE (CONT::*getter)() const, void (CONT::*setter)(TYPE const&) >
struct metafield_fun {};
struct test_field {};
struct test
{
int testing() const { return 5; }
void testing(int const&) {}
};
template < typename T >
struct field_writable : boost::mpl::identity<T> {};
template < typename CONT, typename NAME, typename TYPE, TYPE (CONT::*getter)() const >
struct field_writable< metafield_fun<CONT,NAME,TYPE,getter,0> > : boost::mpl::false_
{};
typedef metafield_fun<test, test_field, int, &test::testing, 0> unwritable;
int main()
{
std::cout << typeid(field_writable<unwritable>::type).name() << std::endl;
std::cin.get();
}
The output is always the type passed to, never bool_.
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1 answer
As a working alternative without the conversion issues mentioned in the comments:
struct rw_tag {};
struct ro_tag {};
template<typename CONT, typename NAME, typename TYPE,
TYPE (CONT::*getter)() const, void (CONT::*setter)(TYPE const&)>
struct metafield_fun_rw : rw_tag {};
template<typename CONT, typename NAME, typename TYPE,
TYPE (CONT::*getter)() const>
struct metafield_fun_ro : ro_tag {};
template<class T> struct field_writable
: boost::mpl::bool_< boost::is_base_of<rw_tag, T>::value >
// or just derive directly from: boost::is_base_of<rw_tag, T>::value
{};
typedef metafield_fun_ro<test, test_field, int, &test::testing> unwritable;
Alternatively metafield_fun
can also typedef
readwrite- / readonly-tags depending on its arguments and field_writable
output conditionally, say using boost::mpl::if_
.
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