replace std::ranges::iota_view by a custom equivalent

Author: alxbilger

Sofa/Component/SolidMechanics/FEM/HyperElastic/src/sofa/component/solidmechanics/fem/hyperelastic/TetrahedronHyperelasticityFEMDrawing.h

@@ -116,7 +116,7 @@ void drawHyperelasticTets(const core::visual::VisualParams* vparams,
                           core::topology::BaseMeshTopology* topology,
                           const std::string& materialName)
 {
-    const auto indices = std::ranges::iota_view(static_cast<sofa::Size>(0), topology->getNbTetrahedra());
+    const auto indices = sofa::helper::IotaView(static_cast<sofa::Size>(0), topology->getNbTetrahedra());
     drawHyperelasticTets<DataTypes>(vparams, x, topology, materialName, indices);
 }
 

Sofa/framework/Core/src/sofa/core/visual/DrawMesh.h

@@ -24,6 +24,7 @@
 #include <sofa/core/config.h>
 #include <sofa/core/topology/BaseMeshTopology.h>
 #include <sofa/core/topology/Topology.h>
+#include <sofa/helper/IotaView.h>
 #include <sofa/helper/visual/DrawTool.h>
 
 #include <ranges>
@@ -66,7 +67,7 @@ struct BaseDrawMesh
         const ColorContainer& colors = Derived::defaultColors)
     {
         const auto totalNbElements = topology->getNbElements<typename Derived::ElementType>();
-        const auto elementsToDraw = std::ranges::iota_view(static_cast<decltype(totalNbElements)>(0), totalNbElements);
+        const auto elementsToDraw = sofa::helper::IotaView(static_cast<decltype(totalNbElements)>(0), totalNbElements);
         drawSomeElements(drawTool, position, topology, elementsToDraw, colors);
     }
 

Sofa/framework/Helper/CMakeLists.txt

@@ -70,6 +70,7 @@ set(HEADER_FILES
     ${SRC_ROOT}/hash.h
     ${SRC_ROOT}/init.h
     ${SRC_ROOT}/integer_id.h
+    ${SRC_ROOT}/IotaView.h
     ${SRC_ROOT}/accessor/ReadAccessor.h
     ${SRC_ROOT}/accessor/ReadAccessorFixedArray.h
     ${SRC_ROOT}/accessor/ReadAccessorVector.h

Sofa/framework/Helper/src/sofa/helper/IotaView.h

@@ -0,0 +1,53 @@
+#pragma once
+
+#include <iterator>
+
+namespace sofa::helper
+{
+
+/**
+ * Simple alternative to std::ranges::iota_view, compatible with pre-C++20
+ */
+template <typename T>
+class IotaView
+{
+public:
+    struct iota_iterator
+    {
+        using value_type = T;
+        using difference_type = std::ptrdiff_t;
+        using iterator_category = std::forward_iterator_tag;
+        using reference = T&;
+        using pointer = T*;
+
+        explicit iota_iterator(T val) : val_(val) {}
+
+        T operator*() const { return val_; }
+        iota_iterator& operator++() { ++val_; return *this; }
+        bool operator!=(const iota_iterator& other) const { return val_ != other.val_; }
+
+    private:
+        T val_;
+    };
+
+    using iterator = iota_iterator;
+    using value_type = T;
+
+    IotaView(T start, T end) : m_start(start), m_end(end) {}
+
+    iterator begin() const { return iterator(m_start); }
+    iterator end() const { return iterator(m_end); }
+
+    [[nodiscard]] T size() const { return m_end - m_start; }
+    [[nodiscard]] T operator[](T i) const { return m_start + i; }
+    T front() const { return m_start; }
+    T back() const { return m_end - 1; }
+    [[nodiscard]] bool empty() const { return m_start == m_end; }
+
+private:
+    T m_start;
+    T m_end;
+};
+
+
+}

Sofa/framework/Helper/test/CMakeLists.txt

@@ -5,6 +5,7 @@ project(Sofa.Helper_test)
 set(SOURCE_FILES
     DiffLib_test.cpp
     Factory_test.cpp
+    IotaView_test.cpp
     KdTree_test.cpp
     NameDecoder_test.cpp
     OptionsGroup_test.cpp

Sofa/framework/Helper/test/IotaView_test.cpp

@@ -0,0 +1,44 @@
+#include <sofa/helper/IotaView.h>
+#include <gtest/gtest.h>
+
+namespace sofa
+{
+
+TEST(IotaView, loop)
+{
+    const auto range = sofa::helper::IotaView{0, 10};
+
+    int i = 0;
+    for (const auto value : range)
+    {
+        EXPECT_EQ(value, i);
+        ++i;
+    }
+}
+
+TEST(IotaView, empty)
+{
+    {
+        const auto range = sofa::helper::IotaView{0, 10};
+        EXPECT_FALSE(range.empty());
+    }
+    {
+        const auto range = sofa::helper::IotaView{0, 0};
+        EXPECT_TRUE(range.empty());
+    }
+}
+
+TEST(IotaView, size)
+{
+    const auto range = sofa::helper::IotaView{0, 10};
+    EXPECT_EQ(range.size(), 10);
+}
+
+TEST(IotaView, access)
+{
+    const auto range = sofa::helper::IotaView{4, 10};
+    EXPECT_EQ(range[0], 4);
+    EXPECT_EQ(range[9], 4+9);
+}
+
+}