You recently asked about legitimate uses of template meta-programming.
This really boils down to phase-distinction and inlining. Let's assume
that you have a rather complicated function of type:
f: (int, t1, t2, t3, ... tN) -> (),
that calls several internal functions g1, ..., gN, and that the first
argument is used to select different pieces of code, like:
if a == 1 then
(* Do one thing *)
else if a == 2 then
(* Do something else. *)
end;
g2 ();
if a == 2 then
(* Do something yet different. *)
In this case, using template meta-programming, I can force the compiler
to generate several different versions of f, by instantiate templates
e.g., f<1>, f<2>, ... f<M>, with the hope that inlining and constant
expression elimination will improve the execution speed of the program
(elimination of branches is very useful):
def f'(a : int, v1: t1, ..., vN : tN) =
case a of
1 : return f<1>(v1, ..., vn);
2 : return f<2>(v1, ..., vn);
3 : return f<3>(v1, ..., vn);
else: return f<>(a, v1, ...., vn);
I think the phase-distinction in meta-template programming is sometimes
an under-appreciated feature.
Thanks,
PKE.
--
Pål-Kristian Engstad ([EMAIL PROTECTED]),
Lead Graphics & Engine Programmer,
Naughty Dog, Inc., 1601 Cloverfield Blvd, 6000 North,
Santa Monica, CA 90404, USA. Ph.: (310) 633-9112.
"It is better to have 100 functions operate on one data structure
than 10 functions on 10 data structures." -- NN
_______________________________________________
bitc-dev mailing list
[email protected]
http://www.coyotos.org/mailman/listinfo/bitc-dev
