Where are the function address literals in c++?
- by academicRobot
First of all, maybe literals is not the right term for this concept, but its the closest I could think of (not literals in the sense of functions as first class citizens).
<UPDATE>
After some reading with help from answer by Chris Dodd, what I'm looking for is literal function addresses as template parameters. Chris' answer indicates how to do this for standard functions, but how can the addresses of member functions be used as template parameters? Since the standard prohibits non-static member function addresses as template parameters (c++03 14.3.2.3), I suspect the work around is quite complicated. Any ideas for a workaround?
Below the original form of the question is left as is for context.
</UPDATE>
The idea is that when you make a conventional function call, it compiles to something like this:
callq <immediate address>
But if you make a function call using a function pointer, it compiles to something like this:
mov <memory location>,%rax
callq *%rax
Which is all well and good. However, what if I'm writing a template library that requires a callback of some sort with a specified argument list and the user of the library is expected to know what function they want to call at compile time? Then I would like to write my template to accept a function literal as a template parameter. So, similar to
template <int int_literal>
struct my_template {...};`
I'd like to write
template <func_literal_t func_literal>
struct my_template {...};
and have calls to func_literal within my_template compile to callq <immediate address>.
Is there a facility in C++ for this, or a work around to achieve the same effect? If not, why not (e.g. some cataclysmic side effects)? How about C++0x or another language?
Solutions that are not portable are fine. Solutions that include the use of member function pointers would be ideal. I'm not particularly interested in being told "You are a <socially unacceptable term for a person of low IQ>, just use function pointers/functors." This is a curiosity based question, and it seems that it might be useful in some (albeit limited) applications.
It seems like this should be possible since function names are just placeholders for a (relative) memory address, so why not allow more liberal use (e.g. aliasing) of this placeholder.
p.s. I use function pointers and functions objects all the the time and they are great. But this post got me thinking about the don't pay for what you don't use principle in relation to function calls, and it seems like forcing the use of function pointers or similar facility when the function is known at compile time is a violation of this principle, though a small one.
Edit
The intent of this question is not to implement delegates, rather to identify a pattern that will embed a conventional function call, (in immediate mode) directly into third party code, possibly a template.
