mutation through restriction

Author: alfC

include/boost/multi/restriction.hpp

@@ -108,7 +108,13 @@ struct bind_front_t {
 
 	// bind_front_t(multi::index idx, Proj& proj) : idx_{idx}, proj_{proj} {}
 	template<class... Args>
-	BOOST_MULTI_HD constexpr auto operator()(Args&&... rest) const noexcept { return proj_(idx_, std::forward<Args>(rest)...); }
+	BOOST_MULTI_HD constexpr auto operator()(Args&&... rest) const& noexcept { return proj_(idx_, std::forward<Args>(rest)...); }
+
+	template<class... Args>
+	BOOST_MULTI_HD constexpr auto operator()(Args&&... rest)& noexcept { return proj_(idx_, std::forward<Args>(rest)...); }
+
+	template<class... Args>
+	BOOST_MULTI_HD constexpr auto operator()(Args&&... rest)&& noexcept { return proj_(idx_, std::forward<Args>(rest)...); }
 };
 
 template<dimensionality_type D, class Proj>
@@ -419,6 +425,18 @@ class restriction : std::conditional_t<std::is_reference_v<Proj>, detail::non_co
 		}
 	}
 
+	BOOST_MULTI_HD constexpr auto operator[](index idx) & -> decltype(auto) {
+		// assert( extent().contains(idx) );
+		if constexpr(D != 1) {
+			// auto ll = [idx, proj = proj_](auto... rest) { return proj(idx, rest...); };
+			// return restriction<D - 1, decltype(ll)>(extents_t<D - 1>(xs_.base().tail()), ll);
+			// return [idx, proj = proj_](auto... rest) noexcept { return proj(idx, rest...); } ^ extents_t<D - 1>(xs_.base().tail());
+			return bind_front_t<Proj>{idx, proj_} ^ extents_t<D - 1>(xs_.base().tail());
+		} else {
+			return proj_(idx);
+		}
+	}
+
 	BOOST_MULTI_HD constexpr auto operator[](index idx) const& -> decltype(auto) {
 		// assert( extent().contains(idx) );
 		if constexpr(D != 1) {

test/flattened.cpp

@@ -314,6 +314,16 @@ auto main() -> int {  // NOLINT(readability-function-cognitive-complexity,bugpro
 		BOOST_TEST( arr.elements()[2] == 2 );
 		// BOOST_TEST( arr.elements()[3] = 22 );  // doesn't compile, good
 	}
+	{
+		multi::array<double, 3> arr = {
+			{{1.0, 2.0, 3.0}, {4.0, 5.0, 6.0}},
+			{{1.0, 2.0, 3.0}, {4.0, 5.0, 6.0}},
+			{{1.0, 2.0, 3.0}, {4.0, 5.0, 6.0}},
+			{{1.0, 2.0, 3.0}, {4.0, 5.0, 6.0}}
+		};
+
+		BOOST_TEST( arr.flattened().size() == 8 );
+	}
 
 	return boost::report_errors();
 }

test/restrictions.cpp

@@ -8,6 +8,8 @@
 #include <boost/multi/array.hpp>
 #include <boost/multi/elementwise.hpp>
 
+#include <boost/multi/detail/what.hpp>
+
 #include <algorithm>   // IWYU pragma: keep  // for std::equal
 #include <cmath>       // for std::abs
 #include <concepts>    // for constructible_from  // NOLINT(misc-include-cleaner)  // IWYU pragma: keep
@@ -300,6 +302,30 @@ auto main() -> int {
 		multi::array<double, 3> arr;
 		arr = [](auto i, auto j, auto k) { return static_cast<double>(i + j + k); } ^ multi::extents_t<3>(2, 3, 4);
 	}
+	{
+		std::vector<int> vec = {1, 2, 3};
+
+		auto&& arr = [&vec](auto i) -> int& { return vec[i];} ^ multi::extents_t<1>(vec.size());
+
+		// multi::detail::what(arr[1], arr[1][1]);
+		arr[1] = 99;
+
+		BOOST_TEST( vec[1] == 99 );
+	}
+
+	// {
+	// 	std::vector<std::vector<int>> vvec = {
+	// 		{1, 2, 3},
+	// 		{4, 5, 6}
+	// 	};
+
+	// 	auto&& arr = [p = &vvec](auto i, auto j) -> int& { return (*p)[i][j];} ^ multi::extents_t<2>(vvec.size(), vvec.front().size());
+
+	// 	// multi::detail::what(arr[1], arr[1][1]);
+	// 	arr[1][1] = 99;
+
+	// 	BOOST_TEST( vvec[1][1] == 99 );
+	// }
 
 	return boost::report_errors();
 }