I worked up a much better example of what I'm trying to do:
///////////////////////////////////////////////////////////////////////
//////////////////////////////
#include <iostream>
#include
#include
using namespace std;
template <typename T>
struct MyValueType
{
typedef MyValueType<T> self_type;
MyValueType() {}
MyValueType(self_type const & v) {}
template <typename V>
MyValueType(V const & v,
typename boost::enable_if<
boost::is_convertible >::type * dummy = 0)
{
cout << "MyValueType template constructor 1" << endl;
}
template <typename V>
MyValueType(V const & v,
typename boost::disable_if<
boost::is_convertible >::type * dummy = 0)
{
cout << "MyValueType template constructor 2" << endl;
}
};
template <typename T>
struct MyContainer
{
typedef T value_type;
typedef MyContainer<T> self_type;
MyContainer() {}
MyContainer(MyContainer const & c) {}
template <typename C>
MyContainer(C const & c,
typename boost::enable_if<
boost::is_convertible
>::type * dummy = 0)
{
cout << "MyContainer template constructor 1" << endl;
}
template <typename C>
MyContainer(C const & c,
typename boost::disable_if<
boost::is_convertible
>::type * dummy = 0)
{
cout << "MyContainer template constructor 2" << endl;
}
};
typedef MyValueType<int> integer_value;
typedef MyValueType<double> real_value;
typedef MyContainer integer_container;
typedef MyContainer real_container;
int main()
{
integer_container ic;
real_container rc(ic);
return 0;
};
///////////////////////////////////////////////////////////////////////
//////////////////////////////
In this case, compiling with the first set of typedefs results in the
following errors:
/boost/boost/utility/enable_if.hpp: In instantiation of
'boost::disable_if, void>':
boost/boost/type_traits/is_convertible.hpp:128: instantiated from
'boost::detail::is_convertible_basic_impl'
/boost/boost/type_traits/is_convertible.hpp:228: instantiated from
'boost::detail::is_convertible_impl
'
/boost/boost/type_traits/is_convertible.hpp:302: instantiated from
'boost::detail::is_convertible_impl_dispatch'
/boost/boost/type_traits/is_convertible.hpp:348: instantiated from
'boost::is_convertible'
/boost/boost/utility/enable_if.hpp:36: instantiated from
'boost::enable_if, void>'
test.cpp:72: instantiated from here (**This is the call to the copy
constructor in main()**)
/boost/boost/utility/enable_if.hpp:59: error: incomplete type
'boost::is_convertible' used in
nested name specifier
From what I can tell, this looks like the same problem that I was
having in the much simpler example -- the compiler wants to instantiate
is_convertible, and in order to do this, it
needs the constructors in MyValueType, which are themselves
enabled/disabled with enable_if<> and disable_if<>.
Is there a way that I can make this work without having to resort to
using is_same<> (which works, but doesn't capture the sematics that I
need)?
Thanks again,
Tim
On Sep 6, 2006, at 1:13 PM, Tim Robertson wrote:
In retrospect, this was probably too trivial an example to give you --
I realize that it's silly to want to use enable_if<> to do what the
compiler can do for itself. There's a far more complex situation
behind the question, but I'm having trouble distilling it down to a
question of reasonable length...
