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Pointer-to-member as template argument

Hi all!

I'm writing a luabind/boost::python-like binding utility for a Squirrel
language to generating wrapper-functions for C++ classes and have a
problem with passing the pointer-to-member argument and deducing the
type of them.

I want to make a library which I can use like that:

class_<fs::path , sq_filesystem:: ttag>(v, "path", no_base)
.constructor<co nst char*>()
.def("native_fi le_string", &fs::path::nati ve_file_string)

I didn't have problems with contructor - I've just write a specialized
constructor for each type:

// base template
template<typena me Class, int TypeTag, typename Sig>
struct sq_constructor {};

// const char* constructor template
template<class Class, int TypeTag>
struct sq_constructor< Class, TypeTag, const char*>
static int implementation( HSQUIRRELVM v)
if (sq_gettype(v, 2) == OT_STRING)
const char * sz;
sq_getstring(v, 2, &sz);
Class * o = new Class(sz);
sq_setinstanceu p(v, 1, o);
return 0;
return sq_throwerror(v , "invalid param - string expected");

and implement a _class::method:

template<class Class, unsigned int TypeTag>
class class_
// adding a constructor
template<class Sig>
inline class_& constructor()
sq_register("co nstructor",
sq_constructor< Class, TypeTag, Sig>::implement ation



But with creating method wrapper I have a problem. When I wrote:

template<typena me Class, int TypeTag, typename Sig, Sig Method>
struct sq_method {};

template<class Class, int TypeTag, std::string (Class::*Method )() const>
struct sq_method<Class , TypeTag, std::string (Class::*)() const, Method>

static int implementation( HSQUIRRELVM v)
Class * o;

// sq_pushstring(v , o->*Method().c_st r(), -1);
return 1;

template<class Class, unsigned int TypeTag>
class class_

// adding a method
template<class Sig>
inline class_& def(const SQChar * name, Sig func)
sq_register(nam e, sq_method<Class , TypeTag, Sig, func>::implemen tation);


I had error in class_::def() on template resolution:

`func' is not a valid template argument
error: it must be a pointer-to-member of
the form `&X::Y'

and "`<type error>' is not a class type"

What I'm doing wrong?
Adam Dziendziel, Poland
Jul 23 '05 #1
1 4505
Thing that I have noticed:

typedef std::string (fs::path::*fty pe)(void) const;

// works
f = &sq_method<fs:: path, 3334, ftype,
&fs::path::nati ve_file_string> ::implementatio n;

// doesn't work
ftype p = &fs::path::nati ve_file_string;
f = &sq_method<fs:: path, 3334, ftype, p>::implementat ion;

GCC 3.3.1 produces:
error: `p' is not a valid template argument
error: it must be a pointer-to-member of the form `&X::Y'

But I must pass the pointer through the .def() method of class_ which
fills the first three template parameters and hide this ugly syntax.
How can I do it?
Adam -Nalfein- Dziendziel, Poland

Jul 23 '05 #2

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