Re: [Boost-users] Constant floats

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 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 wrote:

...

Robert Dailey 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.

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