From 1254ee74108c731484566b858b9dc34d2391d323 Mon Sep 17 00:00:00 2001
From: Joel Falcou <jfalcou@codereckons.com>
Date: Thu, 30 Oct 2025 08:57:44 +0100
Subject: [PATCH] Fix rvalue handling in block

See merge request oss/rotgen!46
---
 include/rotgen/container/block/dynamic.hpp |  26 ++
 include/rotgen/container/block/fixed.hpp   |  17 ++
 include/rotgen/detail/helpers.hpp          |  13 +-
 include/rotgen/functions/extract.hpp       | 281 ++++++++++++---------
 4 files changed, 207 insertions(+), 130 deletions(-)

diff --git a/include/rotgen/container/block/dynamic.hpp b/include/rotgen/container/block/dynamic.hpp
index 9ed70b2..504a15e 100644
--- a/include/rotgen/container/block/dynamic.hpp
+++ b/include/rotgen/container/block/dynamic.hpp
@@ -139,6 +139,32 @@ namespace rotgen
     {
     }
 
+    block(Ref&& r, Index i0, Index j0, Index ni, Index nj)
+    requires(!requires { typename Ref::rotgen_block_tag; } && !is_immutable)
+      : parent(r.base(), i0, j0, ni, nj)
+    {
+    }
+
+    block(Ref&& r, Index i0, Index j0, Index ni, Index nj)
+    requires(requires { typename Ref::rotgen_block_tag; } && !is_immutable)
+      : parent(r.base(), i0, j0, ni, nj)
+    {
+    }
+
+    block(Ref&& r, Index i0, Index j0)
+    requires(!requires { typename Ref::rotgen_block_tag; } && Rows != -1 &&
+             Cols != -1 && !is_immutable)
+      : parent(r.base(), i0, j0, Rows, Cols)
+    {
+    }
+
+    block(Ref&& r, Index i0, Index j0)
+    requires(requires { typename Ref::rotgen_block_tag; } && Rows != -1 &&
+             Cols != -1 && !is_immutable)
+      : parent(r.base(), i0, j0, Rows, Cols)
+    {
+    }
+
     block(parent const& base) : parent(base) {}
 
     bool is_contiguous_linear() const
diff --git a/include/rotgen/container/block/fixed.hpp b/include/rotgen/container/block/fixed.hpp
index df4d148..64016a5 100644
--- a/include/rotgen/container/block/fixed.hpp
+++ b/include/rotgen/container/block/fixed.hpp
@@ -133,11 +133,28 @@ namespace rotgen
     {
     }
 
+    block(Ref&& r, Index i0, Index j0, Index ni, Index nj)
+    requires(!is_immutable)
+      : parent(r.base(), i0, j0, ni, nj)
+    {
+    }
+
+    block(Ref&& r, Index i0, Index j0)
+    requires(Rows != -1 && Cols != -1 && !is_immutable)
+      : parent(r.base(), i0, j0, Rows, Cols)
+    {
+    }
+
     template<typename B, Index R, Index C, bool I, int FS>
     block(block<B, R, C, I, FS> const& other) : parent(other.base())
     {
     }
 
+    template<typename B, Index R, Index C, bool I, int FS>
+    block(block<B, R, C, I, FS>&& other) : parent(other.base())
+    {
+    }
+
     template<typename OtherDerived>
     block(Eigen::MatrixBase<OtherDerived> const& other) : parent(other)
     {
diff --git a/include/rotgen/detail/helpers.hpp b/include/rotgen/detail/helpers.hpp
index f700640..17fd00c 100644
--- a/include/rotgen/detail/helpers.hpp
+++ b/include/rotgen/detail/helpers.hpp
@@ -11,6 +11,8 @@
 
 #include <type_traits>
 
+#define ROTGEN_FWD(...) static_cast<decltype(__VA_ARGS__)&&>(__VA_ARGS__)
+
 namespace rotgen::detail
 {
   template<typename T> constexpr int static_size()
@@ -50,14 +52,7 @@ namespace rotgen::detail
   inline constexpr bool has_same_vector_size = []() {
     // No vector = noo size
     if (!(M::IsVectorAtCompileTime && N::IsVectorAtCompileTime)) return false;
-    // Row vectors -> same Cols
-    if (M::RowsAtCompileTime == 1 && N::RowsAtCompileTime == 1)
-      return M::ColsAtCompileTime == N::ColsAtCompileTime;
-    // Col vectors -> same Rows
-    if (M::ColsAtCompileTime == 1 && N::ColsAtCompileTime == 1)
-      return M::RowsAtCompileTime == N::RowsAtCompileTime;
-    // Mixing 1xN with Mx1
-    return false;
+    else return static_size<M>() == static_size<N>();
   }();
 
   template<typename T>
@@ -65,7 +60,7 @@ namespace rotgen::detail
     std::conditional_t<std::remove_cvref_t<T>::is_immutable ||
                          std::is_const_v<T>,
                        std::add_const_t<std::remove_cvref_t<T>>,
-                       std::remove_cvref_t<T>>;
+                       std::remove_reference_t<T>>;
 
   template<auto M, auto N>
   inline constexpr auto select_static = (M == -1 || N == -1) ? -1 : M;
diff --git a/include/rotgen/functions/extract.hpp b/include/rotgen/functions/extract.hpp
index 46d4633..73e7e4f 100644
--- a/include/rotgen/functions/extract.hpp
+++ b/include/rotgen/functions/extract.hpp
@@ -8,12 +8,14 @@
 #pragma once
 #include <rotgen/detail/helpers.hpp>
 
+#include <type_traits>
+
 namespace rotgen
 {
   namespace detail
   {
     template<concepts::entity Entity>
-    void validate_extract([[maybe_unused]] Entity& e,
+    void validate_extract([[maybe_unused]] Entity const& e,
                           [[maybe_unused]] Index i0,
                           [[maybe_unused]] Index j0,
                           [[maybe_unused]] Index ni,
@@ -28,260 +30,297 @@ namespace rotgen
 
   //======================== EXTRACT ========================
   template<concepts::entity Entity>
-  auto extract(Entity& e, Index i0, Index j0, Index ni, Index nj)
+  auto extract(Entity&& e, Index i0, Index j0, Index ni, Index nj)
   {
     detail::validate_extract(e, i0, j0, ni, nj);
-    if constexpr (requires { e.as_map(); })
-      return extract(e.as_map(), i0, j0, ni, nj);
-    else return block<detail::propagate_const<Entity>>(e, i0, j0, ni, nj);
+    if constexpr (requires { ROTGEN_FWD(e).as_map(); })
+      return extract(ROTGEN_FWD(e).as_map(), i0, j0, ni, nj);
+    else
+      return block<detail::propagate_const<Entity>>(ROTGEN_FWD(e), i0, j0, ni,
+                                                    nj);
   }
 
   template<Index NI, Index NJ, concepts::entity Entity>
   requires(NI != -1 && NJ != -1)
-  auto extract(Entity& e, Index i0, Index j0)
+  auto extract(Entity&& e, Index i0, Index j0)
   {
     detail::validate_extract(e, i0, j0, NI, NJ);
-    if constexpr (requires { e.as_map(); })
-      return extract<NI, NJ>(e.as_map(), i0, j0);
-    else return block<detail::propagate_const<Entity>, NI, NJ>(e, i0, j0);
+    if constexpr (requires { ROTGEN_FWD(e).as_map(); })
+      return extract<NI, NJ>(ROTGEN_FWD(e).as_map(), i0, j0);
+    else
+      return block<detail::propagate_const<Entity>, NI, NJ>(ROTGEN_FWD(e), i0,
+                                                            j0);
   }
 
   template<Index NI, Index NJ, concepts::entity Entity>
   requires((NI != -1) != (NJ != -1))
-  auto extract(Entity& e, Index i0, Index j0, Index ni, Index nj)
+  auto extract(Entity&& e, Index i0, Index j0, Index ni, Index nj)
   {
     detail::validate_extract(e, i0, j0, ni, nj);
-    if constexpr (requires { e.as_map(); })
-      return extract<NI, NJ>(e.as_map(), i0, j0, ni, nj);
+    if constexpr (requires { ROTGEN_FWD(e).as_map(); })
+      return extract<NI, NJ>(ROTGEN_FWD(e).as_map(), i0, j0, ni, nj);
     else
-      return block<detail::propagate_const<Entity>, NI, NJ>(e, i0, j0, ni, nj);
+      return block<detail::propagate_const<Entity>, NI, NJ>(ROTGEN_FWD(e), i0,
+                                                            j0, ni, nj);
   }
 
   //======================== TOP LEFT CORNER ========================
   template<concepts::entity Entity>
-  auto topLeftCorner(Entity& e, Index ni, Index nj)
+  auto topLeftCorner(Entity&& e, Index ni, Index nj)
   {
-    return extract(e, 0, 0, ni, nj);
+    return extract(ROTGEN_FWD(e), 0, 0, ni, nj);
   }
 
   template<Index NI, Index NJ, concepts::entity Entity>
-  auto topLeftCorner(Entity& e)
+  auto topLeftCorner(Entity&& e)
   {
-    return extract<NI, NJ>(e, 0, 0);
+    return extract<NI, NJ>(ROTGEN_FWD(e), 0, 0);
   }
 
   //======================== TOP RIGHT CORNER ========================
   template<concepts::entity Entity>
-  auto topRightCorner(Entity& e, Index ni, Index nj)
+  auto topRightCorner(Entity&& e, Index ni, Index nj)
   {
-    return extract(e, 0, e.cols() - nj, ni, nj);
+    return extract(ROTGEN_FWD(e), 0, e.cols() - nj, ni, nj);
   }
 
   template<Index NI, Index NJ, concepts::entity Entity>
-  auto topRightCorner(Entity& e)
+  auto topRightCorner(Entity&& e)
   {
-    return extract<NI, NJ>(e, 0, e.cols() - NJ);
+    return extract<NI, NJ>(ROTGEN_FWD(e), 0, e.cols() - NJ);
   }
 
   //======================== BOTTOM LEFT CORNER ========================
   template<concepts::entity Entity>
-  auto bottomLeftCorner(Entity& e, Index ni, Index nj)
+  auto bottomLeftCorner(Entity&& e, Index ni, Index nj)
   {
-    return extract(e, e.rows() - ni, 0, ni, nj);
+    return extract(ROTGEN_FWD(e), e.rows() - ni, 0, ni, nj);
   }
 
   template<Index NI, Index NJ, concepts::entity Entity>
-  auto bottomLeftCorner(Entity& e)
+  auto bottomLeftCorner(Entity&& e)
   {
-    return extract<NI, NJ>(e, e.rows() - NI, 0);
+    return extract<NI, NJ>(ROTGEN_FWD(e), e.rows() - NI, 0);
   }
 
   //======================== BOTTOM RIGHT CORNER ========================
   template<concepts::entity Entity>
-  auto bottomRightCorner(Entity& e, Index ni, Index nj)
+  auto bottomRightCorner(Entity&& e, Index ni, Index nj)
   {
-    return extract(e, e.rows() - ni, e.cols() - nj, ni, nj);
+    return extract(ROTGEN_FWD(e), e.rows() - ni, e.cols() - nj, ni, nj);
   }
 
   template<Index NI, Index NJ, concepts::entity Entity>
-  auto bottomRightCorner(Entity& e)
+  auto bottomRightCorner(Entity&& e)
   {
-    return extract<NI, NJ>(e, e.rows() - NI, e.cols() - NJ);
+    return extract<NI, NJ>(ROTGEN_FWD(e), e.rows() - NI, e.cols() - NJ);
   }
 
   //======================== TOP ROWS ========================
-  template<concepts::entity Entity> auto topRows(Entity& e, Index ni)
+  template<concepts::entity Entity> auto topRows(Entity&& e, Index ni)
   {
-    if constexpr (Entity::ColsAtCompileTime == -1)
-      return extract(e, 0, 0, ni, e.cols());
-    else return extract<-1, Entity::ColsAtCompileTime>(e, 0, 0, ni, e.cols());
+    if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == -1)
+      return extract(ROTGEN_FWD(e), 0, 0, ni, e.cols());
+    else
+      return extract<-1, std::remove_cvref_t<Entity>::ColsAtCompileTime>(
+        ROTGEN_FWD(e), 0, 0, ni, e.cols());
   }
 
-  template<Index NI, concepts::entity Entity> auto topRows(Entity& e)
+  template<Index NI, concepts::entity Entity> auto topRows(Entity&& e)
   {
-    if constexpr (Entity::ColsAtCompileTime == -1)
-      return extract<NI, -1>(e, 0, 0, NI, e.cols());
-    else return extract<NI, Entity::ColsAtCompileTime>(e, 0, 0);
+    if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == -1)
+      return extract<NI, -1>(ROTGEN_FWD(e), 0, 0, NI, e.cols());
+    else
+      return extract<NI, std::remove_cvref_t<Entity>::ColsAtCompileTime>(
+        ROTGEN_FWD(e), 0, 0);
   }
 
   //======================== MIDDLE ROWS ========================
   template<concepts::entity Entity>
-  auto middleRows(Entity& e, Index i0, Index ni)
+  auto middleRows(Entity&& e, Index i0, Index ni)
   {
-    if constexpr (Entity::ColsAtCompileTime == -1)
-      return extract(e, i0, 0, ni, e.cols());
-    else return extract<-1, Entity::ColsAtCompileTime>(e, i0, 0, ni, e.cols());
+    if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == -1)
+      return extract(ROTGEN_FWD(e), i0, 0, ni, e.cols());
+    else
+      return extract<-1, std::remove_cvref_t<Entity>::ColsAtCompileTime>(
+        ROTGEN_FWD(e), i0, 0, ni, e.cols());
   }
 
   template<Index NI, concepts::entity Entity>
-  auto middleRows(Entity& e, Index i0)
+  auto middleRows(Entity&& e, Index i0)
   {
-    if constexpr (Entity::ColsAtCompileTime == -1)
-      return extract<NI, -1>(e, i0, 0, NI, e.cols());
-    else return extract<NI, Entity::ColsAtCompileTime>(e, i0, 0);
+    if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == -1)
+      return extract<NI, -1>(ROTGEN_FWD(e), i0, 0, NI, e.cols());
+    else
+      return extract<NI, std::remove_cvref_t<Entity>::ColsAtCompileTime>(
+        ROTGEN_FWD(e), i0, 0);
   }
 
   //======================== BOTTOM ROWS ========================
-  template<concepts::entity Entity> auto bottomRows(Entity& e, Index ni)
+  template<concepts::entity Entity> auto bottomRows(Entity&& e, Index ni)
   {
-    if constexpr (Entity::ColsAtCompileTime == -1)
-      return extract(e, e.rows() - ni, 0, ni, e.cols());
+    if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == -1)
+      return extract(ROTGEN_FWD(e), e.rows() - ni, 0, ni, e.cols());
     else
-      return extract<-1, Entity::ColsAtCompileTime>(e, e.rows() - ni, 0, ni,
-                                                    e.cols());
+      return extract<-1, std::remove_cvref_t<Entity>::ColsAtCompileTime>(
+        ROTGEN_FWD(e), e.rows() - ni, 0, ni, e.cols());
   }
 
-  template<Index NI, concepts::entity Entity> auto bottomRows(Entity& e)
+  template<Index NI, concepts::entity Entity> auto bottomRows(Entity&& e)
   {
-    if constexpr (Entity::ColsAtCompileTime == -1)
-      return extract<NI, -1>(e, e.rows() - NI, 0, NI, e.cols());
-    else return extract<NI, Entity::ColsAtCompileTime>(e, e.rows() - NI, 0);
+    if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == -1)
+      return extract<NI, -1>(ROTGEN_FWD(e), e.rows() - NI, 0, NI, e.cols());
+    else
+      return extract<NI, std::remove_cvref_t<Entity>::ColsAtCompileTime>(
+        ROTGEN_FWD(e), e.rows() - NI, 0);
   }
 
   //======================== LEFT COLS ========================
-  template<concepts::entity Entity> auto leftCols(Entity& e, Index nj)
+  template<concepts::entity Entity> auto leftCols(Entity&& e, Index nj)
   {
-    if constexpr (Entity::RowsAtCompileTime == -1)
-      return extract(e, 0, 0, e.rows(), nj);
-    else return extract<Entity::RowsAtCompileTime, -1>(e, 0, 0, e.rows(), nj);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == -1)
+      return extract(ROTGEN_FWD(e), 0, 0, e.rows(), nj);
+    else
+      return extract<std::remove_cvref_t<Entity>::RowsAtCompileTime, -1>(
+        ROTGEN_FWD(e), 0, 0, e.rows(), nj);
   }
 
-  template<Index NJ, concepts::entity Entity> auto leftCols(Entity& e)
+  template<Index NJ, concepts::entity Entity> auto leftCols(Entity&& e)
   {
-    if constexpr (Entity::RowsAtCompileTime == -1)
-      return extract<-1, NJ>(e, 0, 0, e.rows(), NJ);
-    else return extract<Entity::RowsAtCompileTime, NJ>(e, 0, 0);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == -1)
+      return extract<-1, NJ>(ROTGEN_FWD(e), 0, 0, e.rows(), NJ);
+    else
+      return extract<std::remove_cvref_t<Entity>::RowsAtCompileTime, NJ>(
+        ROTGEN_FWD(e), 0, 0);
   }
 
   //======================== MIDDLE COLS ========================
   template<concepts::entity Entity>
-  auto middleCols(Entity& e, Index j0, Index nj)
+  auto middleCols(Entity&& e, Index j0, Index nj)
   {
-    if constexpr (Entity::RowsAtCompileTime == -1)
-      return extract(e, 0, j0, e.rows(), nj);
-    else return extract<Entity::RowsAtCompileTime, -1>(e, 0, j0, e.rows(), nj);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == -1)
+      return extract(ROTGEN_FWD(e), 0, j0, e.rows(), nj);
+    else
+      return extract<std::remove_cvref_t<Entity>::RowsAtCompileTime, -1>(
+        ROTGEN_FWD(e), 0, j0, e.rows(), nj);
   }
 
   template<Index NJ, concepts::entity Entity>
-  auto middleCols(Entity& e, Index j0)
+  auto middleCols(Entity&& e, Index j0)
   {
-    if constexpr (Entity::RowsAtCompileTime == -1)
-      return extract<-1, NJ>(e, 0, j0, e.rows(), NJ);
-    else return extract<Entity::RowsAtCompileTime, NJ>(e, 0, j0);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == -1)
+      return extract<-1, NJ>(ROTGEN_FWD(e), 0, j0, e.rows(), NJ);
+    else
+      return extract<std::remove_cvref_t<Entity>::RowsAtCompileTime, NJ>(
+        ROTGEN_FWD(e), 0, j0);
   }
 
   //======================== RIGHT COLS ========================
-  template<concepts::entity Entity> auto rightCols(Entity& e, Index nj)
+  template<concepts::entity Entity> auto rightCols(Entity&& e, Index nj)
   {
-    if constexpr (Entity::RowsAtCompileTime == -1)
-      return extract(e, 0, e.cols() - nj, e.rows(), nj);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == -1)
+      return extract(ROTGEN_FWD(e), 0, e.cols() - nj, e.rows(), nj);
     else
-      return extract<Entity::RowsAtCompileTime, -1>(e, 0, e.cols() - nj,
-                                                    e.rows(), nj);
+      return extract<std::remove_cvref_t<Entity>::RowsAtCompileTime, -1>(
+        ROTGEN_FWD(e), 0, e.cols() - nj, e.rows(), nj);
     ;
   }
 
-  template<Index NJ, concepts::entity Entity> auto rightCols(Entity& e)
+  template<Index NJ, concepts::entity Entity> auto rightCols(Entity&& e)
   {
-    if constexpr (Entity::RowsAtCompileTime == -1)
-      return extract<-1, NJ>(e, 0, e.cols() - NJ, e.rows(), NJ);
-    else return extract<Entity::RowsAtCompileTime, NJ>(e, 0, e.cols() - NJ);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == -1)
+      return extract<-1, NJ>(ROTGEN_FWD(e), 0, e.cols() - NJ, e.rows(), NJ);
+    else
+      return extract<std::remove_cvref_t<Entity>::RowsAtCompileTime, NJ>(
+        ROTGEN_FWD(e), 0, e.cols() - NJ);
   }
 
   //======================== ROW ========================
-  template<concepts::entity Entity> auto row(Entity& e, Index i0)
+  template<concepts::entity Entity> auto row(Entity&& e, Index i0)
   {
-    if constexpr (Entity::ColsAtCompileTime == -1)
-      return extract<1, -1>(e, i0, 0, 1, e.cols());
-    else return extract<1, Entity::ColsAtCompileTime>(e, i0, 0);
+    if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == -1)
+      return extract<1, -1>(ROTGEN_FWD(e), i0, 0, 1, e.cols());
+    else
+      return extract<1, std::remove_cvref_t<Entity>::ColsAtCompileTime>(
+        ROTGEN_FWD(e), i0, 0);
   }
 
   //======================== COL ========================
-  template<concepts::entity Entity> auto col(Entity& e, Index j0)
+  template<concepts::entity Entity> auto col(Entity&& e, Index j0)
   {
-    if constexpr (Entity::RowsAtCompileTime == -1)
-      return extract<-1, 1>(e, 0, j0, e.rows(), 1);
-    else return extract<Entity::RowsAtCompileTime, 1>(e, 0, j0);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == -1)
+      return extract<-1, 1>(ROTGEN_FWD(e), 0, j0, e.rows(), 1);
+    else
+      return extract<std::remove_cvref_t<Entity>::RowsAtCompileTime, 1>(
+        ROTGEN_FWD(e), 0, j0);
   }
 
   //======================== VECTOR HEAD ========================
   template<concepts::entity Entity>
-  auto head(Entity& e, Index n)
-  requires(Entity::RowsAtCompileTime == 1 || Entity::ColsAtCompileTime == 1)
+  auto head(Entity&& e, Index n)
+  requires(std::remove_cvref_t<Entity>::RowsAtCompileTime == 1 ||
+           std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
   {
-    if constexpr (Entity::RowsAtCompileTime == 1)
-      return extract<1, Dynamic>(e, 0, 0, 1, n);
-    else if constexpr (Entity::ColsAtCompileTime == 1)
-      return extract<Dynamic, 1>(e, 0, 0, n, 1);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == 1)
+      return extract<1, Dynamic>(ROTGEN_FWD(e), 0, 0, 1, n);
+    else if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
+      return extract<Dynamic, 1>(ROTGEN_FWD(e), 0, 0, n, 1);
   }
 
   template<Index N, concepts::entity Entity>
-  auto head(Entity& e)
-  requires(Entity::RowsAtCompileTime == 1 || Entity::ColsAtCompileTime == 1)
+  auto head(Entity&& e)
+  requires(std::remove_cvref_t<Entity>::RowsAtCompileTime == 1 ||
+           std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
   {
-    if constexpr (Entity::RowsAtCompileTime == 1) return extract<1, N>(e, 0, 0);
-    else if constexpr (Entity::ColsAtCompileTime == 1)
-      return extract<N, 1>(e, 0, 0);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == 1)
+      return extract<1, N>(ROTGEN_FWD(e), 0, 0);
+    else if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
+      return extract<N, 1>(ROTGEN_FWD(e), 0, 0);
   }
 
   //======================== VECTOR TAIL ========================
   template<concepts::entity Entity>
-  auto tail(Entity& e, Index n)
-  requires(Entity::RowsAtCompileTime == 1 || Entity::ColsAtCompileTime == 1)
+  auto tail(Entity&& e, Index n)
+  requires(std::remove_cvref_t<Entity>::RowsAtCompileTime == 1 ||
+           std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
   {
-    if constexpr (Entity::RowsAtCompileTime == 1)
-      return extract<1, Dynamic>(e, 0, e.cols() - n, 1, n);
-    else if constexpr (Entity::ColsAtCompileTime == 1)
-      return extract<Dynamic, 1>(e, e.rows() - n, 0, n, 1);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == 1)
+      return extract<1, Dynamic>(ROTGEN_FWD(e), 0, e.cols() - n, 1, n);
+    else if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
+      return extract<Dynamic, 1>(ROTGEN_FWD(e), e.rows() - n, 0, n, 1);
   }
 
   template<Index N, concepts::entity Entity>
-  auto tail(Entity& e)
-  requires(Entity::RowsAtCompileTime == 1 || Entity::ColsAtCompileTime == 1)
+  auto tail(Entity&& e)
+  requires(std::remove_cvref_t<Entity>::RowsAtCompileTime == 1 ||
+           std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
   {
-    if constexpr (Entity::RowsAtCompileTime == 1)
-      return extract<1, N>(e, 0, e.cols() - N);
-    else if constexpr (Entity::ColsAtCompileTime == 1)
-      return extract<N, 1>(e, e.rows() - N, 0);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == 1)
+      return extract<1, N>(ROTGEN_FWD(e), 0, e.cols() - N);
+    else if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
+      return extract<N, 1>(ROTGEN_FWD(e), e.rows() - N, 0);
   }
 
   //======================== VECTOR SEGMENT ========================
   template<concepts::entity Entity>
-  auto segment(Entity& e, Index s, Index n)
-  requires(Entity::RowsAtCompileTime == 1 || Entity::ColsAtCompileTime == 1)
+  auto segment(Entity&& e, Index s, Index n)
+  requires(std::remove_cvref_t<Entity>::RowsAtCompileTime == 1 ||
+           std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
   {
-    if constexpr (Entity::RowsAtCompileTime == 1)
-      return extract<1, Dynamic>(e, 0, s, 1, n);
-    else if constexpr (Entity::ColsAtCompileTime == 1)
-      return extract<Dynamic, 1>(e, s, 0, n, 1);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == 1)
+      return extract<1, Dynamic>(ROTGEN_FWD(e), 0, s, 1, n);
+    else if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
+      return extract<Dynamic, 1>(ROTGEN_FWD(e), s, 0, n, 1);
   }
 
   template<Index N, concepts::entity Entity>
-  auto segment(Entity& e, Index s)
-  requires(Entity::RowsAtCompileTime == 1 || Entity::ColsAtCompileTime == 1)
+  auto segment(Entity&& e, Index s)
+  requires(std::remove_cvref_t<Entity>::RowsAtCompileTime == 1 ||
+           std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
   {
-    if constexpr (Entity::RowsAtCompileTime == 1) return extract<1, N>(e, 0, s);
-    else if constexpr (Entity::ColsAtCompileTime == 1)
-      return extract<N, 1>(e, s, 0);
+    if constexpr (std::remove_cvref_t<Entity>::RowsAtCompileTime == 1)
+      return extract<1, N>(ROTGEN_FWD(e), 0, s);
+    else if constexpr (std::remove_cvref_t<Entity>::ColsAtCompileTime == 1)
+      return extract<N, 1>(ROTGEN_FWD(e), s, 0);
   }
 }