Re: Compile time executed functions

[Robert A Duff <bobduff@world.std.com>]

Jean-Marc Bourguet <jbourguet@free.fr> writes:

> My question? Me comparing C++ and Ada?  I think you are confusing me
> with somebody else. I came into this thread when you asked for an
> example of using template in C++ for computing things at compile time to
> give you one.  Then you asked for a formal guarantee that it was
> computed at compile time.  The level at which the C++ standard describe
> semantic make it impossible to have such guarantee.  Do you have a
> formal guarantee that an Ada compiler does not generate a function to
> calculate the 10! when you use the litteral 3628800?  I don't think so
> and there is no such guarantee for C++. What the C++ standard does is
> constraint the expression to be a constant integer expression and allows
> the defined named and such expressions to be used in place like case
> labels, array sizes and template parameters where no C++ programmer
> would expect the expression be evaluated at run-time, where no sane C++
> compiler would evaluate the expression at run-time. 

Right.  In fact, a C++ compiler would have to go to some extra trouble
to evaluate these sorts of things at run time, so it's safe to say that
it doesn't.

> Some seems to think that the biggest difference between Ada generic and
> C++ template is the fact that the templates are instanciated
> automatically or that they are constrained by use.  My point of view is
> that these differences are syntaxic differences and do not modify
> significantly the expressing power.  I think that the ability to
> specialize template is a point where the C++ templates are more
> powerfull than the Ada generics.

Also, Ada generics can't be recursive.

- Bob