Amit's 1d->2d matrix that I can base a rewrite of mine on.

scratchpad/amitmatrix.hpp

@@ -26,17 +26,18 @@ namespace amt {
 			base_type data;
 			size_type size;
 
-          constexpr auto operator[](size_type k) const noexcept {
+			constexpr reference operator[](size_type k) noexcept requires (!IsConst) {
 				assert(k < size && "Out of bound access");
 				return data[k];
 			}
 
-          constexpr auto operator[](size_type k) noexcept requires (!IsConst) {
+			constexpr const_reference operator[](size_type k) const noexcept {
 				assert(k < size && "Out of bound access");
 				return data[k];
 			}
 		};
 
+
 		constexpr Matrix() noexcept = default;
 		constexpr Matrix(Matrix const&) = default;
 		constexpr Matrix& operator=(Matrix const&) = default;

tests/matrix2.cpp

@@ -0,0 +1,52 @@
+#include <catch2/catch_test_macros.hpp>
+#include <fmt/core.h>
+#include <string>
+#include "rand.hpp"
+#include "scratchpad/amitmatrix.hpp"
+#include "worldbuilder.hpp"
+#include <iostream>
+#include <numeric>
+#include <algorithm>
+
+using namespace fmt;
+using std::string;
+
+inline void random_matrix(amt::Matrix<int> &out) {
+  for(size_t y = 0; y < out.rows(); y++) {
+    for(size_t x = 0; x < out.cols(); x++) {
+      out[y][x] = Random::uniform<int>(-10,10);
+    }
+  }
+}
+
+TEST_CASE("basic matrix iterator", "[matrix2:basic]") {
+  size_t width = Random::uniform<size_t>(5, 11);
+  size_t height = Random::uniform<size_t>(3, 13);
+
+  amt::Matrix<int> test{height,width,0};
+  random_matrix(test);
+
+  println("FIRST RANDOM");
+  std::cout << test << std::endl;
+
+  for(auto cell : test) {
+    print("{} ", cell);
+  }
+
+  println("DIRECT ACCESS");
+  for(size_t y = 0; y < test.rows(); y++) {
+    for(size_t x = 0; x < test.cols(); x++) {
+      print("{} ", test(x, y));
+    }
+  }
+
+  auto filled = test;
+  std::fill(filled.begin(), filled.end(), 8);
+  println("SECOND FILLED");
+  std::cout << filled << std::endl;
+
+  auto iota_style = filled;
+  std::iota(iota_style.begin(), iota_style.end(), 0);
+  println("THIRD IOTA");
+  std::cout << iota_style << std::endl;
+}