From a3d72c89b7cdee920e37d0bfc9de1d2c3c9c3f7f Mon Sep 17 00:00:00 2001
From: Arash Badie-Modiri <arashbm@gmail.com>
Date: Sun, 20 Jul 2025 22:51:16 +0300
Subject: [PATCH] CSVReader should satisfy input_range

---
 .github/workflows/cmake-multi-platform.yml |  2 +
 include/internal/common.hpp                |  4 ++
 include/internal/csv_reader.hpp            |  2 +
 tests/CMakeLists.txt                       |  1 +
 tests/test_csv_ranges.cpp                  | 57 ++++++++++++++++++++++
 5 files changed, 66 insertions(+)
 create mode 100644 tests/test_csv_ranges.cpp

diff --git a/.github/workflows/cmake-multi-platform.yml b/.github/workflows/cmake-multi-platform.yml
index e2cce85..56a2a11 100644
--- a/.github/workflows/cmake-multi-platform.yml
+++ b/.github/workflows/cmake-multi-platform.yml
@@ -26,6 +26,7 @@ jobs:
         os: [windows-latest, ubuntu-latest]
         build_type: [Release]
         c_compiler: [gcc, cl]
+        cxx_standard: [17, 20]
         include:
           - os: windows-latest
             c_compiler: cl
@@ -57,6 +58,7 @@ jobs:
       # See https://cmake.org/cmake/help/latest/variable/CMAKE_BUILD_TYPE.html?highlight=cmake_build_type
       run: >
         cmake -B ${{ steps.strings.outputs.build-output-dir }}
+        -DCSV_CXX_STANDARD=${{ matrix.cxx_standard }}
         -DCMAKE_CXX_COMPILER=${{ matrix.cpp_compiler }}
         -DCMAKE_C_COMPILER=${{ matrix.c_compiler }}
         -DCMAKE_BUILD_TYPE=${{ matrix.build_type }}
diff --git a/include/internal/common.hpp b/include/internal/common.hpp
index 4b943db..d94a34e 100644
--- a/include/internal/common.hpp
+++ b/include/internal/common.hpp
@@ -54,6 +54,10 @@ namespace csv {
 
 #define STATIC_ASSERT(x) static_assert(x, "Assertion failed")
 
+#if (defined(CMAKE_CXX_STANDARD) && CMAKE_CXX_STANDARD == 20) || __cplusplus >= 202002L
+#define CSV_HAS_CXX20
+#endif
+
 #if (defined(CMAKE_CXX_STANDARD) && CMAKE_CXX_STANDARD == 17) || __cplusplus >= 201703L
 #define CSV_HAS_CXX17
 #endif
diff --git a/include/internal/csv_reader.hpp b/include/internal/csv_reader.hpp
index 300e7da..98f2f45 100644
--- a/include/internal/csv_reader.hpp
+++ b/include/internal/csv_reader.hpp
@@ -82,9 +82,11 @@ namespace csv {
 
             /** Access the CSVRow held by the iterator */
             CONSTEXPR_14 reference operator*() { return this->row; }
+            CONSTEXPR_14 reference operator*() const { return const_cast<reference>(this->row); }
 
             /** Return a pointer to the CSVRow the iterator has stopped at */
             CONSTEXPR_14 pointer operator->() { return &(this->row); }
+            CONSTEXPR_14 pointer operator->() const { return const_cast<pointer>(&(this->row)); }
 
             iterator& operator++();   /**< Pre-increment iterator */
             iterator operator++(int); /**< Post-increment iterator */
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index e5b57a8..7ddd9a5 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -27,6 +27,7 @@ target_sources(csv_test
         test_data_type.cpp
         test_raw_csv_data.cpp
         test_round_trip.cpp
+        test_csv_ranges.cpp
     )
 target_link_libraries(csv_test csv)
 target_link_libraries(csv_test Catch2::Catch2WithMain)
diff --git a/tests/test_csv_ranges.cpp b/tests/test_csv_ranges.cpp
new file mode 100644
index 0000000..258e132
--- /dev/null
+++ b/tests/test_csv_ranges.cpp
@@ -0,0 +1,57 @@
+#include <catch2/catch_all.hpp>
+#include <csv.hpp>
+
+#ifdef CSV_HAS_CXX20
+#include <ranges>
+
+TEST_CASE("CSVReader C++20 Ranges Compatibility", "[ranges][cxx20]") {
+    SECTION("CSVReader works with std::ranges::distance") {
+        std::stringstream ss("A,B,C\n1,2,3\n4,5,6\n7,8,9");
+        csv::CSVReader reader(ss);
+
+        auto count = std::ranges::distance(reader);
+        REQUIRE(count == 3);
+    }
+
+    SECTION("CSVReader works with std::views") {
+        std::stringstream ss("A,B,C\n1,2,3\n4,5,6\n7,8,9\n10,11,12");
+        csv::CSVReader reader(ss);
+
+        auto filtered = reader |
+                        std::views::filter([](const csv::CSVRow &row) {
+                            return !row.empty() && row[0].get<int>() > 5;
+                        });
+
+        int filtered_count = 0;
+        for (const auto &row : filtered) {
+            filtered_count++;
+            int val = row[0].get<int>();
+            REQUIRE(val > 5);
+        }
+        REQUIRE(filtered_count == 2); // rows with 7 and 10
+    }
+
+    SECTION("CSVReader iterator satisfies input_range requirements") {
+        std::stringstream ss("A,B\n1,2\n3,4");
+        csv::CSVReader reader(ss);
+
+        auto it = reader.begin();
+        auto end = reader.end();
+
+        static_assert(std::input_iterator<decltype(it)>);
+        static_assert(std::ranges::range<csv::CSVReader>);
+        static_assert(std::ranges::input_range<csv::CSVReader>);
+        static_assert(std::sentinel_for<decltype(end), decltype(it)>);
+
+        REQUIRE(it != end);
+        auto row = *it;
+        REQUIRE(row.size() == 2);
+
+        ++it;
+        REQUIRE(it != end);
+
+        ++it;
+        REQUIRE(it == end);
+    }
+}
+#endif