dlib C++ Library - num_nonnegative_weights.h

// Copyright (C) 2012 Davis E. King (davis@dlib.net)
// License: Boost Software License See LICENSE.txt for the full license.
#ifndef DLIB_NUM_NONNEGATIVE_WEIGHtS_Hh_
#define DLIB_NUM_NONNEGATIVE_WEIGHtS_Hh_
#include "../enable_if.h"
namespace dlib
{
 namespace impl2
 {
 template <
 typename T,
 unsigned long (T::*funct)()const
 >
 struct hnnf_helper
 {
 typedef char type;
 };
 template <typename T>
 char has_num_nonnegative_weights_helper( typename hnnf_helper<T,&T::num_nonnegative_weights>::type = 0 ) { return 0;}
 struct two_bytes
 {
 char a[2]; 
 };
 template <typename T>
 two_bytes has_num_nonnegative_weights_helper(int) { return two_bytes();}
 template <typename T>
 struct work_around_visual_studio_bug
 {
 const static unsigned long U = sizeof(has_num_nonnegative_weights_helper<T>('a'));
 };
 // This is a template to tell you if a feature_extractor has a num_nonnegative_weights function or not.
 template <typename T, unsigned long U = work_around_visual_studio_bug<T>::U > 
 struct has_num_nonnegative_weights 
 {
 static const bool value = false;
 };
 template <typename T>
 struct has_num_nonnegative_weights <T,1>
 {
 static const bool value = true;
 };
 }
 // call fe.num_nonnegative_weights() if it exists, otherwise return 0.
 template <typename feature_extractor>
 typename enable_if<impl2::has_num_nonnegative_weights<feature_extractor>,unsigned long>::type num_nonnegative_weights (
 const feature_extractor& fe
 )
 {
 return fe.num_nonnegative_weights();
 }
 template <typename feature_extractor>
 typename disable_if<impl2::has_num_nonnegative_weights<feature_extractor>,unsigned long>::type num_nonnegative_weights (
 const feature_extractor& /*fe*/
 )
 {
 return 0;
 }
}
#endif // DLIB_NUM_NONNEGATIVE_WEIGHtS_Hh_