Add test for std::pair

Closes #17

Author: hahnjo

types/README.md

@@ -1,6 +1,7 @@
 # Types
 
  * [`fundamental`](fundamental): fundamental column types
+ * [`pair`](pair): `std::pair` with different element types
  * [`string`](string): `std::string` with all `[Split]Index{32,64}` column types
  * [`variant`](variant): `std::variant` with `Switch` column type
  * [`vector`](vector): `std::vector` with all `[Split]Index{32,64}` column types

types/pair/README.md

@@ -0,0 +1,14 @@
+# `std::pair`
+
+## Fields
+
+ * `Int32_String`: `std::pair<std::int32_t, std::string>`
+ * `Int32_Vector`: `std::pair<std::int32_t, std::vector<std::int32_t>>`
+ * `String_Vector`: `std::pair<std::string, std::vector<std::int32_t>>`
+
+with the default column types.
+
+## Entries
+
+1. Simple values
+2. Zero / empty values

types/pair/read.C

@@ -0,0 +1,91 @@
+#include <ROOT/REntry.hxx>
+#include <ROOT/RNTupleReader.hxx>
+
+using ROOT::Experimental::REntry;
+using ROOT::Experimental::RNTupleReader;
+
+#include <cstdint>
+#include <fstream>
+#include <ostream>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
+
+using Vector = std::vector<std::int32_t>;
+
+template <typename T> static void PrintValue(const T &value, std::ostream &os);
+
+template <> void PrintValue(const std::int32_t &value, std::ostream &os) {
+  os << value;
+}
+
+template <> void PrintValue(const std::string &value, std::ostream &os) {
+  os << "\"" << value << "\"";
+}
+
+template <> void PrintValue(const Vector &value, std::ostream &os) {
+  os << "[";
+  bool first = true;
+  for (auto element : value) {
+    if (first) {
+      first = false;
+    } else {
+      os << ",";
+    }
+    os << "\n        " << element;
+  }
+  if (!value.empty()) {
+    os << "\n      ";
+  }
+  os << "]";
+}
+
+template <typename T, typename U>
+static void PrintPairValue(const REntry &entry, std::string_view name,
+                           std::ostream &os, bool last = false) {
+  auto &value = *entry.GetPtr<std::pair<T, U>>(name);
+  os << "    \"" << name << "\": [\n";
+  os << "      ";
+  PrintValue(value.first, os);
+  os << ",\n";
+  os << "      ";
+  PrintValue(value.second, os);
+  os << "\n";
+  os << "    ]";
+  if (!last) {
+    os << ",";
+  }
+  os << "\n";
+}
+
+void read(std::string_view input = "types.pair.root",
+          std::string_view output = "types.pair.json") {
+  std::ofstream os(std::string{output});
+  os << "[\n";
+
+  auto reader = RNTupleReader::Open("ntpl", input);
+  auto &entry = reader->GetModel().GetDefaultEntry();
+  bool first = true;
+  for (auto index : *reader) {
+    reader->LoadEntry(index);
+
+    if (first) {
+      first = false;
+    } else {
+      os << ",\n";
+    }
+    os << "  {\n";
+
+    PrintPairValue<std::int32_t, std::string>(entry, "Int32_String", os);
+    PrintPairValue<std::int32_t, Vector>(entry, "Int32_Vector", os);
+    PrintPairValue<std::string, Vector>(entry, "String_Vector", os,
+                                        /*last=*/true);
+
+    os << "  }";
+    // Newline is intentionally missing, may need to print a comma before the
+    // next entry.
+  }
+  os << "\n";
+  os << "]\n";
+}

types/pair/write.C

@@ -0,0 +1,48 @@
+#include <ROOT/RField.hxx>
+#include <ROOT/RNTupleModel.hxx>
+#include <ROOT/RNTupleUtil.hxx>
+#include <ROOT/RNTupleWriteOptions.hxx>
+#include <ROOT/RNTupleWriter.hxx>
+
+using ROOT::Experimental::EColumnType;
+using ROOT::Experimental::RField;
+using ROOT::Experimental::RNTupleModel;
+using ROOT::Experimental::RNTupleWriteOptions;
+using ROOT::Experimental::RNTupleWriter;
+
+#include <cstdint>
+#include <memory>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
+
+using Vector = std::vector<std::int32_t>;
+
+void write(std::string_view filename = "types.pair.root") {
+  auto model = RNTupleModel::Create();
+
+  auto Int32_String =
+      model->MakeField<std::pair<std::int32_t, std::string>>("Int32_String");
+  auto Int32_Vector =
+      model->MakeField<std::pair<std::int32_t, Vector>>("Int32_Vector");
+  auto String_Vector =
+      model->MakeField<std::pair<std::string, Vector>>("String_Vector");
+
+  RNTupleWriteOptions options;
+  options.SetCompression(0);
+  auto writer =
+      RNTupleWriter::Recreate(std::move(model), "ntpl", filename, options);
+
+  // First entry: simple values
+  *Int32_String = {1, "abc"};
+  *Int32_Vector = {2, {1, 2, 3}};
+  *String_Vector = {"def", {4, 5, 6}};
+  writer->Fill();
+
+  // Second entry: zero / empty values
+  *Int32_String = {0, ""};
+  *Int32_Vector = {0, {}};
+  *String_Vector = {"", {}};
+  writer->Fill();
+}