From 123c325ff52405252ac0422eb0085684ed83629a Mon Sep 17 00:00:00 2001
From: Pierre Dejoue <pierre.dejoue@gmail.com>
Date: Fri, 18 Aug 2023 10:38:40 +0200
Subject: [PATCH] Update stdutils::span

---
 src/stdutils/include/stdutils/span.h | 45 +++++++++++++++++++++++++++-
 src/tests/stdutils/src/test_span.cpp | 20 +++++++++++--
 2 files changed, 62 insertions(+), 3 deletions(-)

diff --git a/src/stdutils/include/stdutils/span.h b/src/stdutils/include/stdutils/span.h
index 86b1da9..5909775 100644
--- a/src/stdutils/include/stdutils/span.h
+++ b/src/stdutils/include/stdutils/span.h
@@ -2,13 +2,22 @@
 
 #include <cassert>
 #include <cstddef>
+#include <limits>
+#include <type_traits>
+
 
 namespace stdutils
 {
 
+inline constexpr std::size_t dyn_extent = std::numeric_limits<std::size_t>::max();  // -1
+
 // Imitation of std::span in C++20
+
+template <typename T, std::size_t Sz = dyn_extent, class Enable = void>
+class span {};
+
 template <typename T>
-class span
+class span<T, dyn_extent, void>
 {
 public:
     span(T* ptr, std::size_t size) noexcept : m_ptr(ptr), m_size(size) { assert(m_ptr); }
@@ -23,8 +32,10 @@ class span
 
     std::size_t size() const { return m_size; }
 
+    T* data() { return m_ptr; }
     T* begin() { return m_ptr; }
     T* end() { return m_ptr + m_size; }
+    const T* data() const { return m_ptr; }
     const T* begin() const { return m_ptr; }
     const T* end() const { return m_ptr + m_size; }
 
@@ -36,4 +47,36 @@ class span
     std::size_t m_size;
 };
 
+template <typename T, std::size_t Sz>
+class span<T, Sz, std::enable_if_t<Sz != dyn_extent>>
+{
+    using this_type = span<T, Sz, std::enable_if_t<Sz != dyn_extent>>;
+public:
+    explicit span(T* ptr) noexcept : m_ptr(ptr) { assert(m_ptr); }
+    span(const this_type&) noexcept = default;
+    span(this_type&&) noexcept = default;
+    this_type& operator=(const this_type&) noexcept = default;
+    this_type& operator=(this_type&&) noexcept = default;
+
+    // For qualification conversions (e.g. non-const T to const T)
+    template <typename R>
+    span(const span<R, Sz, void>& other) noexcept : m_ptr(other.begin()) { assert(m_ptr); }
+
+    constexpr std::size_t size() const { return Sz; }
+
+    T* data() { return m_ptr; }
+    T* begin() { return m_ptr; }
+    T* end() { return m_ptr + Sz; }
+    const T* data() const { return m_ptr; }
+    const T* begin() const { return m_ptr; }
+    const T* end() const { return m_ptr + Sz; }
+
+    T& operator[](std::size_t idx) { assert(idx < Sz); return *(m_ptr + idx); }
+    const T& operator[](std::size_t idx) const { assert(idx < Sz); return *(m_ptr + idx); }
+
+private:
+    T* m_ptr;
+};
+
+
 } // namespace stdutils
\ No newline at end of file
diff --git a/src/tests/stdutils/src/test_span.cpp b/src/tests/stdutils/src/test_span.cpp
index 205856a..b8e68d9 100644
--- a/src/tests/stdutils/src/test_span.cpp
+++ b/src/tests/stdutils/src/test_span.cpp
@@ -1,13 +1,14 @@
 #include <catch_amalgamated.hpp>
+
 #include <stdutils/span.h>
 
 #include <vector>
 
-TEST_CASE("span<T> to span<const T>", "[span]")
+TEST_CASE("Dynamic extent span<T> to span<const T>", "[span]")
 {
     std::vector<int> test_vect { 0, 2, 3, 4 };
 
-    auto span = stdutils::span(test_vect.data(), test_vect.size());
+    auto span = stdutils::span<int>(test_vect.data(), test_vect.size());
     span[0] = 1;
     CHECK(test_vect[0] == 1);
 
@@ -15,3 +16,18 @@ TEST_CASE("span<T> to span<const T>", "[span]")
     CHECK(const_span[0] == 1);
     CHECK(const_span.size() == test_vect.size());
 }
+
+TEST_CASE("Static extent span<T> to span<const T>", "[span]")
+{
+    std::vector<int> test_vect { 1, 2, 3, 4 };
+
+    auto span = stdutils::span<int, 2>(test_vect.data() + 2);
+    REQUIRE(span.size() == 2);
+    span[0] = 0;
+    CHECK(test_vect[2] == 0);
+
+    auto const_span = stdutils::span<const int, 2>(span);
+    REQUIRE(const_span.size() == 2);
+    CHECK(const_span[0] == 0);
+    CHECK(const_span[1] == 4);
+}