boost fusion: strange problem depending on number

问题:

I am trying to use Boost::Fusion (Boost v1.42.0) in a personal project. I get an interesting error with this code:

#include "boost/fusion/include/sequence.hpp"
#include "boost/fusion/include/make_vector.hpp"
#include "boost/fusion/include/insert.hpp"
#include "boost/fusion/include/invoke_procedure.hpp"
#include "boost/fusion/include/make_vector.hpp"
#include <iostream>

class Class1
{ 
    public:
    typedef boost::fusion::vector<int,float,float,char,int,int> SequenceType;
    SequenceType s;
        Class1(SequenceType v):s(v){}
};

class Class2
{
    public:
    Class2(){}
    void met(int a,float b ,float c ,char d ,int e,int f)
    {
        std::cout << a << " " << b << " " << c << " " << d << " " << e << std::endl;
    }
};

int main(int argn, char**)
{
Class2 p;
Class1 t(boost::fusion::make_vector(9,7.66f,8.99f,'s',7,6));
boost::fusion::begin(t.s); //OK
boost::fusion::insert(t.s, boost::fusion::begin(t.s), &p); //OK
boost::fusion::invoke_procedure(&Class2::met,boost::fusion::insert(t.s, boost::fusion::begin(t.s), &p)); //FAILS
}

It fails to compile (gcc 4.4.1):

In file included from /home/thechaos/Escriptori/of_preRelease_v0061_linux_FAT/addons/ofxTableGestures/ext/boost/fusion/include/invoke_procedur
e.hpp:10,
                 from problema concepte.cpp:11:
/home/thechaos/Escriptori/of_preRelease_v0061_linux_FAT/addons/ofxTableGestures/ext/boost/fusion/functional/invocation/invoke_procedure.hpp: I
n function ‘void boost::fusion::invoke_procedure(Function, const Sequence&) [with Function = void (Class2::*)(int, float, float, char, int, in
t), Sequence = boost::fusion::joint_view<boost::fusion::joint_view<boost::fusion::iterator_range<boost::fusion::vector_iterator<const boost::f
usion::vector<int, float, float, char, int, int, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_>, 0>, 
boost::fusion::vector_iterator<boost::fusion::vector<int, float, float, char, int, int, boost::fusion::void_, boost::fusion::void_, boost::fus
ion::void_, boost::fusion::void_>, 0> >, const boost::fusion::single_view<Class2*> >, boost::fusion::iterator_range<boost::fusion::vector_iter
ator<boost::fusion::vector<int, float, float, char, int, int, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion:
:void_>, 0>, boost::fusion::vector_iterator<const boost::fusion::vector<int, float, float, char, int, int, boost::fusion::void_, boost::fusion
::void_, boost::fusion::void_, boost::fusion::void_>, 6> > >]’:
problema concepte.cpp:39:   instantiated from here
/home/thechaos/Escriptori/of_preRelease_v0061_linux_FAT/addons/ofxTableGestures/ext/boost/fusion/functional/invocation/invoke_procedure.hpp:88
: error: incomplete type ‘boost::fusion::detail::invoke_procedure_impl<void (Class2::*)(int, float, float, char, int, int), const boost::fusio
n::joint_view<boost::fusion::joint_view<boost::fusion::iterator_range<boost::fusion::vector_iterator<const boost::fusion::vector<int, float, f
loat, char, int, int, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_>, 0>, boost::fusion::vector_itera
tor<boost::fusion::vector<int, float, float, char, int, int, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::
void_>, 0> >, const boost::fusion::single_view<Class2*> >, boost::fusion::iterator_range<boost::fusion::vector_iterator<boost::fusion::vector<
int, float, float, char, int, int, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_>, 0>, boost::fusion:
:vector_iterator<const boost::fusion::vector<int, float, float, char, int, int, boost::fusion::void_, boost::fusion::void_, boost::fusion::voi
d_, boost::fusion::void_>, 6> > >, 7, true, false>’ used in nested name specifier

However, if I change the number of arguments in the vectors and the method from 6 to 5 from int,float,float,char,int,int to int,float,float,char,int,I can compile it without problems.

I suspected about the maximum number of arguments being a limitation, but I tried to change it through defining FUSION_MAX_VECTOR_SIZE without success.

I am unable to see what am I doing wrong. Can you reproduce this? Can it be a boost bug (i doubt it but is not impossible)?

回答1:

Yes indeed, you need to change some iteration limits. You're just changing the wrong one. :)

What you need to define is BOOST_FUSION_INVOKE_PROCEDURE_MAX_ARITY; by default, it is 6. You obviously need 7 (but might as well bump it to 10):

#define BOOST_FUSION_INVOKE_PROCEDURE_MAX_ARITY 10

#include "boost/fusion/include/sequence.hpp"
#include "boost/fusion/include/make_vector.hpp"
#include "boost/fusion/include/insert.hpp"
#include "boost/fusion/include/invoke_procedure.hpp"
#include "boost/fusion/include/make_vector.hpp"
#include <iostream>
.
.
.

There are three total within the invocation domain.

Whenever you're looking for the limit of something, search for "Limits" on the documentation. Choose the one relevant to what you're doing. From there, it tells you the defaults and what the options are.

---

Just concerning the code itself, I should point out there is a push_front function:

#include "boost/fusion/include/push_front.hpp"

// ...

boost::fusion::invoke_procedure(&Class2::met,
                                boost::fusion::push_front(t.s, &p));

So you don't need to do the more verbose insert-at-begin.