From 31eaa14c00e63ffcde231b06f21ea550402eef42 Mon Sep 17 00:00:00 2001
From: xlauko <xlauko@mail.muni.cz>
Date: Wed, 10 Jul 2024 15:05:30 +0200
Subject: [PATCH] core: Add simple ranges::to adaptor.

---
 core/include/gap/core/ranges.hpp | 49 ++++++++++++++++++++++++++++++++
 test/core/ranges.cpp             | 28 +++++++++++++++++-
 2 files changed, 76 insertions(+), 1 deletion(-)

diff --git a/core/include/gap/core/ranges.hpp b/core/include/gap/core/ranges.hpp
index 30f4946..b9957f5 100644
--- a/core/include/gap/core/ranges.hpp
+++ b/core/include/gap/core/ranges.hpp
@@ -43,4 +43,53 @@ namespace gap::ranges
     template< range R >
     using range_value_t = std::iter_value_t< iterator_t< R > >;
 
+    template< typename T >
+    concept has_reserve = requires(T t, std::size_t s) { t.reserve(s); };
+
+    template< typename container_t, std::ranges::input_range R >
+    void move_or_copy_elements(R&& rng, container_t& container) {
+        if constexpr (std::is_rvalue_reference_v< decltype(rng) >) {
+            std::move(std::ranges::begin(rng), std::ranges::end(rng),
+                std::back_inserter(container)
+            );
+        } else {
+            std::copy(std::ranges::begin(rng), std::ranges::end(rng),
+                std::back_inserter(container)
+            );
+        }
+    }
+
+    template< template< typename... > class container_t >
+    struct to_fn {
+        template< std::ranges::input_range R >
+        auto operator()(R&& range) const {
+            using value_type         = std::ranges::range_value_t< R >;
+            using result_container_t = container_t< value_type >;
+
+            result_container_t container;
+
+            if constexpr (has_reserve< result_container_t >) {
+                if constexpr (requires { std::ranges::size(range); }) {
+                    container.reserve(std::ranges::size(range));
+                }
+            }
+
+            move_or_copy_elements(std::forward< R >(range), container);
+            return container;
+        }
+
+        template< std::ranges::input_range R >
+        friend auto operator|(R&& range, const to_fn& to) {
+            return to(std::forward< R >(range));
+        }
+    };
+
+    template< template< typename... > class container_t >
+    inline constexpr to_fn< container_t > to{};
+
+    template< template< typename... > class container_t, std::ranges::input_range R >
+    auto operator|(R&& range, to_fn< container_t > const& to) {
+        return to(std::forward< R >(range));
+    }
+
 } // namespace gap::ranges
diff --git a/test/core/ranges.cpp b/test/core/ranges.cpp
index aefff87..64d29db 100644
--- a/test/core/ranges.cpp
+++ b/test/core/ranges.cpp
@@ -1,9 +1,13 @@
 // Copyright (c) 2022-present, Trail of Bits, Inc.
 
-#include <array>
 #include <doctest/doctest.h>
+
 #include <gap/core/ranges.hpp>
+
+#include <array>
 #include <vector>
+#include <list>
+#include <ranges>
 
 namespace gap::test
 {
@@ -31,4 +35,26 @@ namespace gap::test
         gr::range_value_t< std::vector< dummy > >, std::vector< dummy >::value_type
     >);
 
+    TEST_SUITE("ranges") {
+        TEST_CASE("to vector") {
+            std::vector< int > v = {1, 2, 3, 4, 5};
+            auto v2 = v | gr::to< std::vector >;
+            CHECK(v == v2);
+        }
+
+        TEST_CASE("to list") {
+            std::vector< int > v = {1, 2, 3, 4, 5};
+            auto l = v | gr::to< std::list >;
+
+            CHECK(std::equal(v.begin(), v.end(), l.begin(), l.end()));
+        }
+
+        TEST_CASE("to with filter") {
+            std::vector< int > v = {1, 2, 3, 4, 5};
+            auto v2 = v | std::views::filter([] (int x) { return x % 2 == 0; })
+                        | gr::to< std::vector >;
+            CHECK(v2 == std::vector{2, 4});
+        }
+    }
+
 } // namespace gap::test