Re: Fun with member-function pointers
Default User wrote:
I've been working on a project that implements instrument drivers. The API
uses operation codes to direct behavior. All the drivers are subclasses of a
common ABC. In my implementation, I used a method of mapping the op codes
to handlers for that operation. That was accomplished with pointers to
member functions.
Someone asked me why I didn't have the handler storage and lookup in the
base class. My initial response was that the pointers had different types.
Then I got thinking that such a condition doesn't normally slow us down. So
I created a test case (skipping the map and all).
This worked, in that it built and seem to run ok. I'm not overly thrilled
with the cast necessary to store the func pointer. Does anyone see a
problem? Improvements?
How about the following (untested) code that uses type erasure via
boost(or std) function and bind. This negates the need to have virtual
functions, but works fine even if they are virtual.
#include <boost/bind.hpp>
#include <boost/function.hpp>
#include <map>
struct Driver1
{
int f1(int i) { std::cout << "d1.f1: " << i << "\n"; return i; }
int f2(int i) { std::cout << "d1.f2: " << i << "\n"; return i; }
};
struct Driver2
{
int f1(int i) { std::cout << "d2.f1: " << i << "\n"; return i; }
int f2(int i) { std::cout << "d2.f2: " << i << "\n"; return i; }
};
int main()
{
typedef int OpCode;
typedef boost::function<int (int)> Fnc;
typedef std::map<OpCode, Fnc> FncMap;
Driver1 d1;
Driver2 d2;
FncMap fncMap;
fncMap[123] = boost::bind(&Driver1::f1, &d1, _1);
fncMap[456] = boost::bind(&Driver2::f1, &d1, _1);
fncMap[789] = boost::bind(&Driver2::f2, &d1, _1);
assert(1 == fncMap[123](1));
assert(2 == fncMap[456](2));
assert(3 == fncMap[789](3));
return 0;
}
Jeff