On Thu, Sep 8, 2011 at 11:48 AM, Jared McKee <jared.mckee@gmail.com> wrote:
On Thu, Sep 8, 2011 at 11:29 AM, Jeffrey Lee Hellrung, Jr. <jeffrey.hellrung@gmail.com> wrote:
On Thu, Sep 8, 2011 at 7:46 AM, Jared McKee <jared.mckee@gmail.com> wrote:
On Thu, Sep 8, 2011 at 10:19 AM, Jeffrey Lee Hellrung, Jr. <jeffrey.hellrung@gmail.com> wrote:
On Wed, Sep 7, 2011 at 7:48 PM, Jared McKee <jared.mckee@gmail.com>
wrote:
I would like to determine interest in a possible library submission.
I have written some code which converts a member function and object pointer combination to a free function for use in C style callbacks. It has
some
limitations which I will describe shortly.
The basic idea is to be able to convert:
R (B::*)(T0,T1,…) and B*
to
R (*)(T0,T1,…)
Here's an example usage:
class foo { int x; int test(int v) {return x + v;} };
foo* a = new foo; a->x = 3; int (*f)(int) = delegate(a, &foo::inc); cout << f(4) << endl; // outputs "7"
[...snip implementation notes...]
Here's a discussion about the topic:
http://stackoverflow.com/questions/1840029/passing-functor-as-function-point...
Oh...dear.
From stackoverflow there is a link to http://fscked.org/proj/minihax/autocode/functorptr.cc, where the idea is you have a "mold" (I'd call it a template, but...) for the function signature you want to call like
static bool closure() { Functor *thisptr = (Functor *)MAX_INT; return (*thisptr)(); } And then allocate some memory, copy the executable code from that function mold (ie memcpy(newptr, closure, guess_at_size) and look through that memory, find MAX_INT and replace it with the runtime-obtained 'this' pointer. When I was crazy enough to consider this in the past, I used 0xAD0BEA1D instead of MAX_INT. (ie Adobe Aid, as the photoshop plugin callback spec uses function pointers without the ever-so-useful void * extraData param. Disclaimer: this was NOT when I worked at Adobe, but at a place where we were writing a paint package that supported PS plugins). I would just worry about MAX_INT being too common of a thing to find in bytes of executable. But maybe 0xAD0BEA1D is a valid instruction sequence on some platform. Anyhow.... Now I can _imagine_ doing the same thing, but templatized to get any function signature, but I can't say I'd recommend it. Not for a boost library. Or outside a boost library, for that matter. (I think in our case we eventually went with to thread-local storage, as we just needed a function pointer per thread.) Tony