+/// This function isn't used and is only here to provide better compile errors.
+template <class T, class... Args>
+typename std::enable_if<std::extent<T>::value != 0>::type
+make_unique(Args &&...) = delete;
+
+struct FreeDeleter {
+ void operator()(void* v) {
+ ::free(v);
+ }
+};
+
+template<typename First, typename Second>
+struct pair_hash {
+ size_t operator()(const std::pair<First, Second> &P) const {
+ return std::hash<First>()(P.first) * 31 + std::hash<Second>()(P.second);
+ }
+};
+
+/// A functor like C++14's std::less<void> in its absence.
+struct less {
+ template <typename A, typename B> bool operator()(A &&a, B &&b) const {
+ return std::forward<A>(a) < std::forward<B>(b);
+ }
+};
+
+/// A functor like C++14's std::equal<void> in its absence.
+struct equal {
+ template <typename A, typename B> bool operator()(A &&a, B &&b) const {
+ return std::forward<A>(a) == std::forward<B>(b);
+ }
+};
+
+/// Binary functor that adapts to any other binary functor after dereferencing
+/// operands.
+template <typename T> struct deref {
+ T func;
+ // Could be further improved to cope with non-derivable functors and
+ // non-binary functors (should be a variadic template member function
+ // operator()).
+ template <typename A, typename B>
+ auto operator()(A &lhs, B &rhs) const -> decltype(func(*lhs, *rhs)) {
+ assert(lhs);
+ assert(rhs);
+ return func(*lhs, *rhs);
+ }
+};
+