Re: constants within a namespace
On 01.05.2010 04:36, * forums_mp@hotmail.com:
On Apr 30, 1:00 am, Vladimir Jovic<vladasp...@gmail.com> wrote:
Where and how you place your constant doesn't matter. What your friend
told you is a nonsense. If you add and use constants, your program size
will increase (off course), but what is an alternative? Only not to use
constants- Hide quoted text -
The alternative/recommended form according to him is to put global
constatns in a class (as opposed to a namespace). i.e:
//.h
class GlobalConstants {
public :
static int const X = 5 ;
static double const PI ;
};
//.cpp
double const GlobalConstants::PI = 3.141;
With my approach:
namespace GlobalConstants {
int const X = 5;
double const PI = 3.141 ;
}
I'll end up with defined objects X and PI in every module (since the
members are declared constant and have internal linkage) even if the
module used one and only one of the object.
For a while, I thought elimination of unused symbols was a guarantee
within the standard but I was wrong. I also thought his recommended
form ( a class ) would result in a defined object in every module. I
was wrong. Long story short, it appears the namespace approach is a
QOI issue.
You can always force elimination, within the language rules, if you want that,
without using separate compilation, that is, with the constants (of any types)
defined in the header file.
And this involves putting the constants a class template, which I guess
misleadingly can be described as "in a class".
Goes like (in a header file)
template< Dummy >
struct GlobalConstants_
{
int const x;
double const pi;
};
template< Dummy >
int GlobalConstants_<Dummy>::x = 5;
template< Dummy >
double GlobalConstants_<Dummy>::pi = 3.141;
typedef GlobalConstants_<void> GlobalConstants;
But it's not like it's context-independently "recommended" or anything, or like
any other way of defining constants is context-independently "recommended".
It's just a solution where you do not want a separately compiled file and you do
want guaranteed elimination and/or extern linkage.
Cheers & hth.,
- Alf