[Boost-users] Function pointers vs boost.function

From: Kurt Kohler (kohler_at_[hidden])
Date: 2008-09-02 14:53:58

I have some code that uses pointers to member functions (not
boost.function). It compiles and works fine. But when I tried to convert
the code to use boost.function, I got a mess of errors.
I know I'm doing something wrong, but I have no idea what it is. A clue
would be greatly appreciated.

Here's a reduced test case.

#include <boost/function.hpp>

struct X
{
    double f(double x) { return x; }
    double g(double x) { return -x; }

    //typedef boost::function<double (double)> ftype;
    typedef double (X::*ftype)(double);
    
    double call(ftype func, double x)
    {
        //return func(x);
        return (this->*func)(x);
    }
};

int main(int argc, char *argv[])
{
    X x;
    x.call(&X::f, 1.0);     // Error occurs here
    x.call(&X::g, 2.0);
}

It compiles as it appears above, but if I switch the typedef and return
statements to their commented versions, I get the following errors:

if g++ -DHAVE_CONFIG_H -I. -I/home/kohler/Projects/test/trunk/src -I..
-O0 -Wall -g3 -MT test.0 -MD -MP -MF ".deps/test.Tpo" -c -o test.o
/home/kohler/Projects/test/trunk/src/test.cpp; then mv -f
".deps/test.Tpo" ".deps/test.Po"; else rm -f ".deps/test.Tpo"; exit 1; fi
/usr/include/boost/function/function_template.hpp: In static member
function 'static R
boost::detail::function::function_obj_invoker1<FunctionObj, R,
T0>::invoke(boost::detail::function::function_buffer&, T0) [with
FunctionObj = boost::_mfi::mf1<double, X, double>, R = double, T0 =
double]':
/usr/include/boost/function/function_template.hpp:368: instantiated from
'void boost::detail::function::basic_vtable1<R, T0,
Allocator>::init(FunctionObj, boost::detail::function::function_obj_tag)
[with FunctionObj = boost::_mfi::mf1<double, X, double>, R = double, T0
= double, Allocator = std::allocator<void>]'
/usr/include/boost/function/function_template.hpp:298: instantiated from
'void boost::detail::function::basic_vtable1<R, T0, Allocator>::init(F)
[with F = boost::_mfi::mf1<double, X, double>, R = double, T0 = double,
Allocator = std::allocator<void>]'
/usr/include/boost/function/function_template.hpp:339: instantiated from
'void boost::detail::function::basic_vtable1<R, T0,
Allocator>::init(MemberPtr, boost::detail::function::member_ptr_tag)
[with MemberPtr = double (X::*)(double), R = double, T0 = double,
Allocator = std::allocator<void>]'
/usr/include/boost/function/function_template.hpp:298: instantiated from
'void boost::detail::function::basic_vtable1<R, T0, Allocator>::init(F)
[with F = double (X::*)(double), R = double, T0 = double, Allocator =
std::allocator<void>]'
/usr/include/boost/function/function_template.hpp:277: instantiated from
'boost::detail::function::basic_vtable1<R, T0,
Allocator>::basic_vtable1(F) [with F = double (X::*)(double), R =
double, T0 = double, Allocator = std::allocator<void>]'
/usr/include/boost/function/function_template.hpp:655: instantiated from
'void boost::function1<R, T0, Allocator>::assign_to(Functor) [with
Functor = double (X::*)(double), R = double, T0 = double, Allocator =
std::allocator<void>]'
/usr/include/boost/function/function_template.hpp:513: instantiated from
'boost::function1<R, T0, Allocator>::function1(Functor, typename
boost::enable_if_c<boost::type_traits::ice_not<boost::is_integral<Functor>::value>::value,
int>::type) [with Functor = double (X::*)(double), R = double, T0 =
double, Allocator = std::allocator<void>]'
/usr/include/boost/function/function_template.hpp:753: instantiated from
'boost::function<R ()(T0), Allocator>::function(Functor, typename
boost::enable_if_c<boost::type_traits::ice_not<boost::is_integral<Functor>::value>::value,
int>::type) [with Functor = double (X::*)(double), R = double, T0 =
double, Allocator = std::allocator<void>]'
/home/kohler/Projects/test/trunk/src/test.cpp:21: instantiated from here
/usr/include/boost/function/function_template.hpp:134: error: no match
for call to '(boost::_mfi::mf1<double, X, double>) (double&)'
/usr/include/boost/bind/mem_fn_template.hpp:160: note: candidates are: R
boost::_mfi::mf1<R, T, A1>::operator()(T*, A1) const [with R = double, T
= X, A1 = double]
/usr/include/boost/bind/mem_fn_template.hpp:179: note: R
boost::_mfi::mf1<R, T, A1>::operator()(T&, A1) const [with R = double, T
= X, A1 = double]

g++ -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--with-gxx-include-dir=/usr/include/c++/4.2 --program-suffix=-4.2
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--enable-mpfr --enable-targets=all --enable-checking=release
--build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu
Thread model: posix
gcc version 4.2.3 (Ubuntu 4.2.3-2ubuntu7)