core: added iterable_adaptor

src/entt/core/iterator.hpp

@@ -1,6 +1,7 @@
 #ifndef ENTT_CORE_ITERATOR_HPP
 #define ENTT_CORE_ITERATOR_HPP
 
+#include <iterator>
 #include <memory>
 #include <utility>
 #include "../config/config.h"
@@ -53,6 +54,63 @@ private:
     Type value;
 };
 
+/**
+ * @brief Utility class to create an iterable object from a pair of iterators.
+ * @tparam It Type of iterators.
+ */
+template<typename It>
+struct iterable_adaptor final {
+    /*! @brief Type of the objects returned during iteration. */
+    using value_type = typename std::iterator_traits<It>::value_type;
+    /*! @brief Iterator type. */
+    using iterator = It;
+    /*! @brief Const iterator type. */
+    using const_iterator = It;
+
+    /*! @brief Default constructor. */
+    iterable_adaptor() = default;
+
+    /**
+     * @brief Creates an iterable object from a pair of iterators.
+     * @param from Begin iterator.
+     * @param to End iterator.
+     */
+    iterable_adaptor(It from, It to)
+        : first{from},
+          last{to} {}
+
+    /**
+     * @brief Returns an iterator to the beginning.
+     * @return An iterator to the first element of the range.
+     */
+    [[nodiscard]] const_iterator begin() const ENTT_NOEXCEPT {
+        return first;
+    }
+
+    /*! @copydoc begin */
+    [[nodiscard]] const_iterator cbegin() const ENTT_NOEXCEPT {
+        return begin();
+    }
+
+    /**
+     * @brief Returns an iterator to the end.
+     * @return An iterator to the element following the last element of the
+     * range.
+     */
+    [[nodiscard]] const_iterator end() const ENTT_NOEXCEPT {
+        return last;
+    }
+
+    /*! @copydoc end */
+    [[nodiscard]] const_iterator cend() const ENTT_NOEXCEPT {
+        return end();
+    }
+
+private:
+    It first;
+    It last;
+};
+
 } // namespace entt
 
 #endif

test/entt/core/iterator.cpp

@@ -1,4 +1,5 @@
 #include <utility>
+#include <vector>
 #include <gtest/gtest.h>
 #include <entt/core/iterator.hpp>
 
@@ -20,3 +21,19 @@ TEST(Iterator, InputIteratorPointer) {
     ASSERT_EQ(instance.value, 0);
     ASSERT_EQ(ptr->value, 42);
 }
+
+TEST(Iterator, IterableAdaptor) {
+    std::vector<int> vec{1, 2};
+    entt::iterable_adaptor iterable{vec.begin(), vec.end()};
+    decltype(iterable) other{};
+
+    ASSERT_NO_THROW(other = iterable);
+    ASSERT_NO_THROW(std::swap(other, iterable));
+
+    ASSERT_EQ(iterable.begin(), vec.begin());
+    ASSERT_EQ(iterable.end(), vec.end());
+
+    ASSERT_EQ(*iterable.cbegin(), 1);
+    ASSERT_EQ(*++iterable.cbegin(), 2);
+    ASSERT_EQ(++iterable.cbegin(), --iterable.end());
+}