Re: [Boost-users] Constant floats

From: Robert Dailey (rcdailey_at_[hidden])
Date: 2007-12-11 15:03:32

Sorry, small corrections to my last code example (I had a few typos):

template< typename T >
struct default_alpha;

template<>
struct default_alpha<float>
{
    static const float value = 1.0f; // Note that this is not legal. I'm
simply just presenting pseudo code.
};

template<>
struct default_alpha<unsigned char>
{
    static const unsigned char value = 255;
};

template< typename T >
class Color
{
    Color( T r, T g, T b, T a = default_alpha<T>::value );
};

On Dec 11, 2007 2:01 PM, Robert Dailey <rcdailey_at_[hidden]> wrote:

> Well, the namespace idea won't work either. There's certain details I
> omitted because I wasn't sure if they would be directly related to the
> issue. However I'll go ahead and elaborate now.
>
> I plan to specialize the struct containing the float to determine what
> 'value' I want. For example:
>
> template< typename T >
> struct default_alpha;
>
> template<>
> struct default_alpha<float>
> {
>     static const float alpha = 1.0f;
> };
>
> template<>
> struct default_alpha<unsigned char>
> {
>     static const unsigned char = 255;
> };
>
> So, if I have a 'color' class that takes a template parameter, like below,
> I can use the above specialized structures to figure out how to default
> initialize the 'a' construction parameter.
>
> template< typename T >
> class Color
> {
>     Color( T r, T g, T b, T a = default_alpha<T>::value );
> };
>
> Again, I wasn't sure if these new details were required from the very
> beginning. Apologies for this. Thank you for everyone's continued help.
>
> On Dec 11, 2007 1:14 AM, Roman Perepelitsa <roman.perepelitsa_at_[hidden]>
> wrote:
>
> > Robert Dailey <rcdailey <at> gmail.com> writes:
> > >
> > >
> > > I'm going to be using this float to default-initialize a construction
> > > parameter. For example:
> > > struct default_alpha
> > > {
> > >     static const float value = 1.0f;
> > > };
> > > class foo
> > > {
> > >  foo( float r, float g, float b, float a = default_alpha::value );
> > > };
> > >
> >
> > You can use constant in namespace scope:
> >
> > namespace default_alpha
> > {
> >    static const float value = 1.0f;
> > }
> >
> > HTH,
> > Roman Perepelitsa.
> >
> > _______________________________________________
> > Boost-users mailing list
> > Boost-users_at_[hidden]
> > http://lists.boost.org/mailman/listinfo.cgi/boost-users
> >
>
>