Introduce cartesian product calculating helper

cartesian_product.hh

@@ -0,0 +1,93 @@
+/*
+ * Copyright 2015 Cloudius Systems
+ *
+ */
+
+#pragma once
+
+// Single-pass range over cartesian product of vectors.
+
+// Note:
+//    {a, b, c} x {1, 2} = {{a, 1}, {a, 2}, {b, 1}, {b, 2}, {c, 1}, {c, 2}}
+template<typename T>
+struct cartesian_product {
+    const std::vector<std::vector<T>>& _vec_of_vecs;
+public:
+    class iterator : public std::iterator<std::forward_iterator_tag, std::vector<T>> {
+    public:
+        using value_type = std::vector<T>;
+    private:
+        size_t _pos;
+        const std::vector<std::vector<T>>* _vec_of_vecs;
+        value_type _current;
+        std::vector<typename std::vector<T>::const_iterator> _iterators;
+    public:
+        struct end_tag {};
+        iterator(end_tag) : _pos(-1) {}
+        iterator(const std::vector<std::vector<T>>& vec_of_vecs) : _pos(0), _vec_of_vecs(&vec_of_vecs) {
+            _iterators.reserve(vec_of_vecs.size());
+            for (auto&& vec : vec_of_vecs) {
+                _iterators.push_back(vec.begin());
+                if (vec.empty()) {
+                    _pos = -1;
+                    break;
+                }
+            }
+        }
+        value_type& operator*() {
+            _current.clear();
+            _current.reserve(_vec_of_vecs->size());
+            for (auto& i : _iterators) {
+                _current.emplace_back(*i);
+            }
+            return _current;
+        }
+        void operator++() {
+            ++_pos;
+
+            for (ssize_t i = _iterators.size() - 1; i >= 0; --i) {
+                ++_iterators[i];
+                if (_iterators[i] != (*_vec_of_vecs)[i].end()) {
+                    return;
+                }
+                _iterators[i] = (*_vec_of_vecs)[i].begin();
+            }
+
+            // If we're here it means we've covered every combination
+            _pos = -1;
+        }
+        bool operator==(const iterator& o) const { return _pos == o._pos; }
+        bool operator!=(const iterator& o) const { return _pos != o._pos; }
+    };
+public:
+    cartesian_product(const std::vector<std::vector<T>>& vec_of_vecs) : _vec_of_vecs(vec_of_vecs) {}
+    iterator begin() { return iterator(_vec_of_vecs); }
+    iterator end() { return iterator(typename iterator::end_tag()); }
+};
+
+template<typename T>
+static inline
+size_t cartesian_product_size(const std::vector<std::vector<T>>& vec_of_vecs) {
+    size_t r = 1;
+    for (auto&& vec : vec_of_vecs) {
+        r *= vec.size();
+    }
+    return r;
+}
+
+template<typename T>
+static inline
+bool cartesian_product_is_empty(const std::vector<std::vector<T>>& vec_of_vecs) {
+    for (auto&& vec : vec_of_vecs) {
+        if (vec.empty()) {
+            return true;
+        }
+    }
+    return vec_of_vecs.empty();
+}
+
+template<typename T>
+static inline
+cartesian_product<T> make_cartesian_product(const std::vector<std::vector<T>>& vec_of_vecs) {
+    return cartesian_product<T>(vec_of_vecs);
+}