Dear list,
I have a class Manager that wraps an associative container (e.g. std::map)
and that provides a method that calls a std::find_if to search on the
mapped_type.
template <typename Func>
boost::optional find_if (Func func);
I want to pass free functions, functors, boost::function objects or
boost::lambda expressions to it. There is no problem with free functions
and functors but with boost::function objects (not always) and
boost::lambda expressions. The two lines that do not compile are commented
in the code below. Please find the entire error messages attached.
What am I doing wrong?
Thanks and best regards,
Christian
#include
#include
#include
#include
#include
#include <algorithm>
#include <map>
#include <utility>
template class AssocContainer,
typename Compare = std::less<Key>,
typename Alloc = std::allocator >
class Manager
: public boost::noncopyable
{
public:
typedef AssocContainer AssocCont;
typedef Value value_type;
Manager (const Compare& compare = Compare (),
const Alloc& alloc = Alloc ())
: cont_ (compare, alloc)
{}
~Manager ()
{
cont_.clear ();
}
bool insert (Key key, Value value)
{
return cont_.insert (std::make_pair(key, value)).second;
}
template <typename Func>
boost::optional find_if (Func func)
{
using boost::lambda::_1;
using boost::lambda::bind;
typename AssocCont::iterator findResult =
std::find_if (cont_.begin (), cont_.end (),
bind(func, bind(&AssocCont::value_type::second, _1)));
if (findResult != cont_.end()) {
return boost::optional (findResult->second);
}
return boost::optional ();
}
private:
AssocCont cont_;
};
typedef Manager Container;
bool find42function (const Container::value_type& value)
{
return value == 42;
}
struct Find42functor
: public std::unary_function
{
bool operator () (const Container::value_type& value) const
{
return value == 42;
}
};
int
main ()
{
Container cont;
cont.insert ('a', 42);
// free function -------------------------------------------------------
cont.find_if (&find42function);
boost::function func_1 (&find42function);
cont.find_if (func_1);
// Functor -------------------------------------------------------------
cont.find_if (Find42functor());
Find42functor functor;
boost::function func_2 (functor);
cont.find_if (func_2);
boost::function func_3 = Find42functor();
cont.find_if (func_3);
boost::function func_4 (Find42functor());
//cont.find_if (func_4); // does not compile
/* error message: ========================================================
/d/vendor/include/boost/lambda/detail/function_adaptors.hpp: In static
member function `static Result boost::lambda::function_adaptor::apply(Result (*)(Arg1), A1&) [with RET = boost::function, A1 = int, Arg1 = Find42functor (*)(),
Result = boost::function]':
...
test.cpp:50: instantiated from `boost::optional Manager::find_if(Func) [with Func =
boost::function (*)(Find42functor
(*)()), Key = char, Value = int, AssocContainer = std::map, Compare =
std::less<char>, Alloc = std::allocator >]'
test.cpp:101: instantiated from here
/d/vendor/include/boost/lambda/detail/function_adaptors.hpp:218: error:
invalid conversion from `int' to `Find42functor (*)()'
see error_func_4.txt for the entire error message
========================================================================*/
// lambda --------------------------------------------------------------
using boost::lambda::_1;
boost::function func_5 (_1 == 42);
cont.find_if (func_5);
//cont.find_if (_1 == 42.0); // does not compile
/* error message: =========================================================
/d/vendor/include/boost/lambda/detail/function_adaptors.hpp: In
instantiation of
`boost::lambda::function_adaptor<bool>::sig > >':
...
test.cpp:50: instantiated from `boost::optional Manager::find_if(Func) [with Func =
boost::lambda::lambda_functorboost::lambda::equal_action,
boost::tuples::tuple
, const double, boost::tuples::null_type, boost::tuples::null_type,
boost::tuples::null_type, boost::tuples::null_type,
boost::tuples::null_type, boost::tuples::null_type,
boost::tuples::null_type, boost::tuples::null_type> > >, Key = char, Value
= int, AssocContainer = std::map, Compare = std::less<char>, Alloc =
std::allocator >]'
test.cpp:117: instantiated from here
/d/vendor/include/boost/lambda/detail/function_adaptors.hpp:32: error:
`bool' is not a class, struct, or union type
...
See error_lambda.txt for the entire error message
========================================================================*/
return 0;
}
