slight improve prediction speed

include/LightGBM/tree.h

@@ -138,8 +138,8 @@ public:
     }
   }
 
-  static std::vector<std::function<bool(unsigned int, unsigned int)>> inner_decision_funs;
-  static std::vector<std::function<bool(double, double)>> decision_funs;
+  static std::vector<bool(*)(unsigned int, unsigned int)> inner_decision_funs;
+  static std::vector<bool(*)(double, double)> decision_funs;
 
 private:
   /*!

src/io/tree.cpp

@@ -16,12 +16,11 @@
 
 namespace LightGBM {
 
-std::vector<std::function<bool(unsigned int, unsigned int)>> Tree::inner_decision_funs = 
+std::vector<bool(*)(unsigned int, unsigned int)> Tree::inner_decision_funs =
           {Tree::NumericalDecision<unsigned int>, Tree::CategoricalDecision<unsigned int> };
-std::vector<std::function<bool(double, double)>> Tree::decision_funs = 
+std::vector<bool(*)(double, double)> Tree::decision_funs =
           { Tree::NumericalDecision<double>, Tree::CategoricalDecision<double> };
 
-
 Tree::Tree(int max_leaves)
   :max_leaves_(max_leaves) {