Re: [Boost-users] Functions that evaluate to constants

From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-03-31 13:22:06

AMDG

Robert Dailey wrote:
> Hi,
>
> I realize that C++03 will not permit functions to evaluate down to 
> compile-time constants. However, I cannot wait until C++0x for this 
> feature. So, I'm hoping that Boost will allow a temporary solution. 
> Consider the following structure:
>
> static struct nullptr_t
> {
>     template< typename t_type >
>     operator t_type*() { return 0; }
> } nullptr;
>
> The compiler has everything it needs to turn this code into a single 
> integral constant value. So, if I do the following:
>
> int* foo;
> if( foo == nullptr )
> {
> }
>
>
> Then it should evaluate down to:
>
> int* foo;
> if( foo == 0 )
> {
> }
>
> Is there any way to provide this behavior in Boost? I would like to 
> avoid altering the actual design if possible. Perhaps this actually 
> *does* evaluate to a constant and the problem is that I'm actually 
> unaware of some specific rule that I didn't find in the C++03 
> standard. Thanks.

If you don't need a constant expression, the compiler will probably figure
it out if you compile with optimization.

In Christ,
Steven Watanabe