Merge pull request #258 from dglaeser/feature/generic-reader-direct-open

Feature/generic-reader-immediate-open

CHANGELOG.md

@@ -7,6 +7,7 @@
 
 - __Traits__: support for writing `Dune::FieldMatrix` as tensor field data.
 - __CI__: on PRs, a bunch of performance benchmarks are run with the code of the PR and the target branch, and observed runtime differences are posted as a comment to the pull request.
+- __Reader__: the `Reader` class now allows for opening a file upon instantiation using `GridFormat::Reader::from(filename)` (taking further optional constructor arguments). Moreover, you can now open a file and receive the modified reader as return value using `reader.with_opened(filename)`.
 
 ## Deprecated interfaces
 

README.md

@@ -86,7 +86,7 @@ int main () {
     const auto written_file = writer.write("my_test_file"); // extension is added by the writer
 
     // read the data back in (here we create a generic reader, but you can also select specific ones)
-    GridFormat::Reader reader; reader.open(written_file);
+    auto reader = GridFormat::Reader::from(written_file);
     std::vector<double> cell_field_values(reader.number_of_cells());
     std::vector<double> point_field_values(reader.number_of_points());
     reader.cell_field("cell_field")->export_to(cell_field_values);

gridformat/reader.hpp

@@ -120,6 +120,24 @@ class Reader : public GridReader {
     : _reader{_make_unique(ReaderFactory<FileFormat>::make(f, c))}
     {}
 
+    //! Construct a reader instance from the given arguments, while directly opening the given file
+    template<typename... ConstructorArgs>
+    static Reader from(const std::string& filename, ConstructorArgs&&... args) {
+        return Reader{std::forward<ConstructorArgs>(args)...}.with_opened(filename);
+    }
+
+    //! Read the data from the given file and return this reader
+    Reader& with_opened(const std::string& filename) & {
+        this->open(filename);
+        return *this;
+    }
+
+    //! Read the data from the given file and return this reader (lvalue references overload)
+    Reader&& with_opened(const std::string& filename) && {
+        this->open(filename);
+        return std::move(*this);
+    }
+
  private:
     template<typename ReaderImpl>
     auto _make_unique(ReaderImpl&& reader) const {

test/api/test_generic_reader.cpp

@@ -83,7 +83,6 @@ std::ranges::range auto test_filenames(const std::filesystem::path& folder, cons
 void test_reader(GridFormat::Reader&& reader, const std::string& filename) {
     std::cout << "Testing reader with '" << GridFormat::as_highlight(filename) << "'" << std::endl;
 
-    reader.open(filename);
     const auto points = reader.points()->template export_to<std::vector<std::array<double, 3>>>();
     const auto [_, space_dim] = grid_and_space_dimension(filename);
     const auto get_expected_value = [&] (const std::array<double, 3>& position, double t = 1.0) -> double {
@@ -167,12 +166,21 @@ int test_reader(const std::filesystem::path& folder,
                 ConstructorArgs&&... args) {
     bool visited = false;
     std::ranges::for_each(test_filenames(folder, extension), [&] (const std::string& filename) {
-        test_reader(GridFormat::Reader{std::forward<ConstructorArgs>(args)...}, filename);
+        {
+            GridFormat::Reader reader{std::forward<ConstructorArgs>(args)...};
+            reader.open(filename);
+            test_reader(std::move(reader), filename);
+        }
+        {
+            test_reader(
+                GridFormat::Reader::from(filename, std::forward<ConstructorArgs>(args)...),
+                filename
+            );
+        }
         visited = true;
 
         if (extension == ".vtu") { // exemplarily test that reader propagates names
-            GridFormat::Reader reader{GridFormat::vtu};
-            reader.open(filename);
+            auto reader = GridFormat::Reader{GridFormat::vtu}.with_opened(filename);
             GridFormat::Testing::expect(reader.name() == "VTUReader");
         }
     });