How to create a function pointer for muParser - c++

Question

I would like to define a new function in muParser Link.
The FunctionWrapper-Class should be registrated.
class FunctionWrapper
{
public:
virtual double Evaluate(const double*, int) = 0;
};
The DefineFun-Method needs a string and a function pointer. How can I make this pointer to the function Evaluate?
I would like to call the DefineFun in an other class... something like this:
bool OtherClass::RegisterFunction(std::string name, FunctionWrapper *wrapper)
{
fParser.DefineFun(name, wrapper->????);
}
THx

Answer 1

Have you considered std::function as your wrapper? In conjunction with std::bind or lambdas, it can probably do everything you need. E.g.,
#include <unordered_map>
#include <functional>
#include <exception>
#include <memory>
#include <string>
#include <iostream>
class Evaluator
{
public:
virtual ~Evaluator() {}
virtual double Evaluate( const double*, int ) = 0;
// ...
};
class Registry
{
public:
typedef std::function<double(const double*, int)> Fn; // For easier reading
class NameNotFoundException : public std::exception {};
void Register( const std::string& name, const Fn& fn )
{
_regMap[ name ] = fn;
}
void Call( const std::string& name, const double* const data, const int size )
{
auto it = _regMap.find( name );
if( it == _regMap.end() )
{
throw NameNotFoundException();
}
it->second( data, size ); // Call fn
}
private:
std::unordered_map<std::string, Fn> _regMap;
};
class EvaluatorImpl : public Evaluator
{
public:
double Evaluate( const double* const data, const int size )
{ /*...*/
for( int n=0; n < size; ++n )
std::cout << data[n] << '\n';
return 0;
}
// ...
};
int main()
{
std::shared_ptr<Evaluator> eval( new EvaluatorImpl() );
Registry reg;
// Could use a lambda here instead of std::bind
reg.Register( "Bob",
std::bind( &Evaluator::Evaluate, eval, std::placeholders::_1, std::placeholders::_2 ) );
const double data[] = { 1, 2, 3 };
int size = 3;
reg.Call( "Bob", data, size );
}

Answer 2

here a sample Code:
#include <functional>
#include "muParser.h"
class Evaluator
{
public:
virtual ~Evaluator() {}
virtual double Evaluate( const double*, int ) = 0;
// ...
typedef std::function<double(const double*, int)> Fn; // For easier reading
};
class EvaluatorImpl : public Evaluator
{
public:
double Evaluate( const double* const data, const int size )
{ return 0; }
};
void MyClass::test()
{
Evaluator *e = new EvaluatorImpl();
Evaluator::Fn fn = std::bind( &Evaluator::Evaluate, e, std::placeholders::_1, std::placeholders::_2 );
mu::Parser fParser;
fParser.DefineFun("test", fn);
}
I get no matching function for call to mu::ParserCallback::ParserCallback(std::function<double(const double*, int)>&, bool&)’ when I call DefineFun(string, T a_func)