Re: Compile time executed functions

["Ken Garlington" <Ken.Garlington@computer.org>]

"Jean-Marc Bourguet" <jbourguet@free.fr> wrote in message
news:3AC46252.B7E54EA6@free.fr...
: Ken Garlington wrote:
:
: > Could you post an example of such a template, and what in the C++
standard
: > you rely upon to guarantee compile-time calculations?
:
: First feature, things like
:    enum { foo = x+y*z; }
: are valid as long as x, y and z value are known at compile time and have
: to be evaluated at compile time.

Isn't this usually resolvable as a constant by most Ada compilers? At least
the ones I know will usually do so.

More to the point, does the C++ standard _require_ that foo not generate any
assembly instructions to be executed at run-time? If so, what does it say?

: Second feature it is possible to provide "specialization" for template,
: that is provide a different implementation when some template parameter
: have some constant value.
:
: The first ensure that evaluation is made at compile time.  The second
: that it is possible to make some test.  Looping is available with
: recursion so finally you have a computationnally complete language at
: compile time.  It is painfull to write and even more painfull to use but
: some like abusing the language...
:
: An example, how to compute factorial
:
: #include <iostream>
:
: template <int F>
: struct factorial {
:    enum { RET = factorial<F-1>::RET*F };
: };
:
: template <>
: struct factorial<1> {
:    enum { RET = 1 };
: };
:
: int main() {
:    std::cout << factorial<10>::RET << std::endl;
: }

Are you claiming that this resolves to a single constant value prior to
execution? I don't see how...


: > Also, does
: > "compile-time" include "link-time", or are you not allowed to have
anything
: > in the table that uses addresses?
:
: As some C++ compilers do template instanciation at "link-time", I think
: the answer is yes.

I don't think we're talking about the same thing here...

: -- Jean-Marc