View difference between Paste ID: DbrnL2dK and FQzAZh0n

-//submatrix first version
+//submatrix second version
 
-constexpr Matrix2 submatrix(const Matrix3& m, Matrix3::size_type row_, Matrix3::size_type column_) {
+constexpr value_type operator[](size_type i) const noexcept {
-    assert(row_ < m.rows() && column_ < m.columns() && "invalid submatrix specification. row and column must be inside the input matrix.");
+    assert(i < size());
-    using size_type = Matrix3::size_type;
+    return _data[i];
-    Matrix2 r;
+
-    size_type i = 0;
+constexpr reference operator[](size_type i) noexcept {
-    for (size_type k = 0; k < m.rows(); k++) {
+    assert(i < size());
-        if (k == row_) {
+    return _data[i];
-            continue;
+
 
-        size_type j = 0;
+constexpr size_type index_to_column(size_type index) const noexcept {
-        for (size_type l = 0; l < m.columns(); l++) {
+    assert(index < size());
-            if (l == column_) {
+    return index % columns();
-                continue;
+
-            }
+constexpr size_type index_to_row(size_type index) const noexcept {
-            r(i, j) = m(k, l);
+    assert(index < size());
-            j++;
+    return index / columns();
 }
-        i++;
+
-    }
+constexpr auto submatrix(size_type remove_row, size_type remove_column) const noexcept {
     assert(remove_row < rows() && remove_column < columns() && "submatrix: row and column to remove must be inside the original matrix.");
     Matrix<ROWS - 1, COLUMNS - 1> r;
     uint8_t ri = 0;
     for (size_type i = 0; i < size(); i++) {
         if(index_to_row(i) != remove_row && index_to_column(i) != remove_column) {
             r[ri++] = _data[i];
         }
     }
     return r;
 }
 
 TEST(Matrix, getRowFromIndex) {
     const Matrix3 a{
         1,5,0,
         -3,2,7,
         0,6,-3
     };
     EXPECT_EQ(0, a.index_to_row(0));
     EXPECT_EQ(0, a.index_to_row(2));
     EXPECT_EQ(2, a.index_to_row(6));
     EXPECT_EQ(2, a.index_to_row(8));
 }
 
 TEST(Matrix, getColumnFromIndex) {
     const Matrix3 a{
         1,5,0,
         -3,2,7,
         0,6,-3
     };
     EXPECT_EQ(0, a.index_to_column(0));
     EXPECT_EQ(1, a.index_to_column(1));
     EXPECT_EQ(2, a.index_to_column(2));
     EXPECT_EQ(0, a.index_to_column(6));
     EXPECT_EQ(1, a.index_to_column(7));
     EXPECT_EQ(2, a.index_to_column(8));
 }
 
 TEST(Matrix, submatrixOf3x3is2x2) {
     const Matrix3 a{
         1,5,0,
         -3,2,7,
         0,6,-3
     };
     const Matrix2 truth{
         -3, 2,
         0, 6
     };
     const auto b = submatrix(a, 0, 2);
     const auto c = a.submatrix(0, 2);
     EXPECT_TRUE(b == truth);
     EXPECT_TRUE(c == truth);
 }