Re: [Boost-users] Constant floats

From: Robert Dailey (rcdailey_at_[hidden])
Date: 2007-12-12 10:07:28

Are function calls allowed to default initialize a construction parameter?
Does the compiler turn the function into a constant? How does that work? I
wasn't aware you could do this...

On Dec 11, 2007 8:02 PM, Stjepan Rajko <stipe_at_[hidden]> wrote:

> On Dec 11, 2007 1:03 PM, Robert Dailey <rcdailey_at_[hidden]> wrote:
> >
> > 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 );
> > };
> >
>
> So why not use Jeff Flinn's suggestion:
>
> template< typename T >
> struct default_alpha;
>
> template<>
> struct default_alpha<float>
> {
>    static float value() { return 1.0f; }
> };
>
> template<>
> struct default_alpha<unsigned char>
> {
>    static unsigned char value() { return 255; }
> };
>
> template< typename T >
> class Color
> {
> public:
>    Color( T r, T g, T b, T a = default_alpha<T>::value() );
> };
>
>
> ...?
>
> Stjepan
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