guard SparseVector branch in Row::get<T> to fix non-vector T instantiation

Author: devsimiyu

src/types.h

@@ -278,36 +278,41 @@ struct Row
                 else if constexpr (std::is_same_v<T, SparseVector> &&
                                    std::is_same_v<ArgType, std::shared_ptr<Row>>)
                 {
-                    SparseVector sparse_vector;
+                    if constexpr (std::is_same_v<T, SparseVector>)
+                    {
+                        SparseVector sparse_vector;
 
-                    auto type_field = std::find_if(arg->column_names.begin(), arg->column_names.end(), [](const std::string& col_name) {
-                        return col_name == "type";
-                    });
+                        auto type_field = std::find_if(arg->column_names.begin(), arg->column_names.end(), [](const std::string& col_name) {
+                            return col_name == "type";
+                        });
 
-                    if (type_field == arg->column_names.end() || std::get<int8_t>(arg->values.at(arg->col_index("type"))) != 0)
-                        return sparse_vector;
+                        if (type_field == arg->column_names.end() || std::get<int8_t>(arg->values.at(arg->col_index("type"))) != 0)
+                            return sparse_vector;
 
-                    auto size = std::get<int32_t>(arg->values.at(arg->col_index("size")));
-                    auto indice_array_data = std::get<std::shared_ptr<ArrayData>>(arg->values.at(arg->col_index("indices")));
-                    auto values_array_data = std::get<std::shared_ptr<ArrayData>>(arg->values.at(arg->col_index("values")));
+                        auto size = std::get<int32_t>(arg->values.at(arg->col_index("size")));
+                        auto indice_array_data = std::get<std::shared_ptr<ArrayData>>(arg->values.at(arg->col_index("indices")));
+                        auto values_array_data = std::get<std::shared_ptr<ArrayData>>(arg->values.at(arg->col_index("values")));
 
-                    std::vector<int> indices;
-                    std::vector<double> values;
+                        std::vector<int> indices;
+                        std::vector<double> values;
 
-                    indices.reserve(indice_array_data->elements.size());
-                    values.reserve(values_array_data->elements.size());
+                        indices.reserve(indice_array_data->elements.size());
+                        values.reserve(values_array_data->elements.size());
 
-                    for (int i = 0; i < indice_array_data->elements.size(); i++)
-                    {
-                        indices.push_back(std::get<int32_t>(indice_array_data->elements[i]));
-                    }
+                        for (int i = 0; i < indice_array_data->elements.size(); i++)
+                        {
+                            indices.push_back(std::get<int32_t>(indice_array_data->elements[i]));
+                        }
 
-                    for (int i = 0; i < values_array_data->elements.size(); i++)
-                    {
-                        values.push_back(std::get<double>(values_array_data->elements[i]));
-                    }
+                        for (int i = 0; i < values_array_data->elements.size(); i++)
+                        {
+                            values.push_back(std::get<double>(values_array_data->elements[i]));
+                        }
 
-                    return SparseVector{size, indices, values};
+                        return SparseVector{size, indices, values};
+                    }
+                    else
+                        throw std::runtime_error("unreachable");
                 }
                 else
                 {