Template mode: Fill with zero upon read

Author: franzpoeschel

src/IO/JSON/JSONIOHandlerImpl.cpp

@@ -31,6 +31,7 @@
 
 #include <toml.hpp>
 
+#include <algorithm>
 #include <exception>
 #include <iostream>
 #include <optional>
@@ -957,31 +958,54 @@ void JSONIOHandlerImpl::writeAttribute(
     m_dirty.emplace(file);
 }
 
-void JSONIOHandlerImpl::readDataset(
-    Writable *writable, Parameter<Operation::READ_DATASET> &parameters)
+namespace
 {
-    switch (m_mode)
+    struct FillWithZeroes
     {
-    case IOMode::Template:
-        throw error::WrongAPIUsage(
-            "Cannot write chunks in Template mode of JSON backend.");
-    case IOMode::Dataset:
-        break;
-    }
+        template <typename T>
+        static void call(void *ptr, Extent const &extent)
+        {
+            T *casted = static_cast<T *>(ptr);
+            size_t flattenedExtent = std::accumulate(
+                extent.begin(), extent.end(), 1, [](size_t left, size_t right) {
+                    return left * right;
+                });
+            std::fill_n(casted, flattenedExtent, T{});
+        }
 
+        static constexpr char const *errorMsg =
+            "[JSON Backend] Fill with zeroes.";
+    };
+} // namespace
+
+void JSONIOHandlerImpl::readDataset(
+    Writable *writable, Parameter<Operation::READ_DATASET> &parameters)
+{
     refreshFileFromParent(writable);
     setAndGetFilePosition(writable);
     auto &j = obtainJsonContents(writable);
     verifyDataset(parameters, j);
 
-    try
-    {
-        switchType<DatasetReader>(parameters.dtype, j["data"], parameters);
-    }
-    catch (json::basic_json::type_error &)
+    switch (m_mode)
     {
-        throw std::runtime_error(
-            "[JSON] The given path does not contain a valid dataset.");
+    case IOMode::Template:
+        std::cerr << "[Warning] Cannot read chunks in Template mode of JSON "
+                     "backend. Will fill with zeroes instead."
+                  << std::endl;
+        switchNonVectorType<FillWithZeroes>(
+            parameters.dtype, parameters.data.get(), parameters.extent);
+        return;
+    case IOMode::Dataset:
+        try
+        {
+            switchType<DatasetReader>(parameters.dtype, j["data"], parameters);
+        }
+        catch (json::basic_json::type_error &)
+        {
+            throw std::runtime_error(
+                "[JSON] The given path does not contain a valid dataset.");
+        }
+        break;
     }
 }