Fix error of typical_segment_tree (T = bool); Add utility to gen a function that always returns a constant

Author: Mr-Python-in-China

library/mrpython/sparse_table.hpp

@@ -18,7 +18,7 @@ using std::size_t;
  */
 template <typename T, typename MergeFunction> class sparse_table {
   std::vector<std::vector<T>> table;
-  MergeFunction merge;
+  MergeFunction const merge;
 
  public:
   template <typename InputIterator>

library/mrpython/typical_segment_tree.hpp

@@ -14,12 +14,12 @@ using std::size_t;
  * 一颗 无标记线段树 模板。
  * @tparam T 元素类型
  * @tparam MergeFunction 合并运算函数，对于函数 `F` 应满足结合律
- */ 
+ */
 template <typename T, typename MergeFunction> class typical_segment_tree {
   std::vector<T> data;
   std::vector<size_t> size;
   size_t n;
-  MergeFunction merge;
+  MergeFunction const merge;
   void build(void) {
     data.reserve(2 * n - 1), size.reserve(2 * n - 1);
     for (size_t i = n; i < 2 * n - 1; ++i) {
@@ -34,7 +34,7 @@ template <typename T, typename MergeFunction> class typical_segment_tree {
   template <typename Fun>
   void set_impl(size_t c, Fun const& operate, size_t pos) {
     if (size[pos] == 1) {
-      data[pos] = operate((T const&)data[pos]);
+      data[pos] = operate((typename std::vector<T>::const_reference)data[pos]);
       return;
     }
     size_t m = size[pos * 2 + 1];

library/mrpython/utility.hpp

@@ -33,12 +33,17 @@ struct gcd {
   }
 };
 template <typename Comp> struct compare_iterator {
-  Comp comp;
+  Comp const comp;
   compare_iterator(Comp const& c): comp(c) {}
   template <typename Iterator>
   Iterator operator()(Iterator a, Iterator b) const {
     return comp(*a, *b) ? a : b;
   }
 };
+template <typename T> struct const_function {
+  T const value;
+  const_function(T const& v): value(v) {}
+  template <typename... Args> T operator()(Args...) const { return value; }
+};
 }  // namespace mrpython
 #endif  // MP_LIBRARY_UTILITY_HPP