Function writeVarvalue

pj_datastore/src/derived_engine.cpp:126–201

Write a VarValue to a DataWriter row at (topic, col), coercing to out_kind.

// Write a VarValue to a DataWriter row at (topic, col), coercing to out_kind.
static void writeVarvalue(
    DataWriter& writer, PJ::TopicId tid, std::size_t col, const VarValue& val, StorageKind out_kind) {
  if (out_kind == StorageKind::kString) {
    if (const auto* s = std::get_if<std::string>(&val)) {
      writer.set(tid, col, std::string_view(*s));
    }
    return;
  }

  // Integer→integer fast paths: avoid the lossy double round-trip.
  if (out_kind == StorageKind::kUint64) {
    if (const auto* u = std::get_if<uint64_t>(&val)) {
      writer.set(tid, col, *u);
      return;
    }
    if (const auto* i = std::get_if<int64_t>(&val)) {
      writer.set(tid, col, static_cast<uint64_t>(*i));
      return;
    }
  }
  if (out_kind == StorageKind::kInt64) {
    if (const auto* i = std::get_if<int64_t>(&val)) {
      writer.set(tid, col, *i);
      return;
    }
    if (const auto* u = std::get_if<uint64_t>(&val)) {
      writer.set(tid, col, static_cast<int64_t>(*u));
      return;
    }
  }
  if (out_kind == StorageKind::kInt32) {
    if (const auto* i = std::get_if<int64_t>(&val)) {
      writer.set(tid, col, static_cast<int32_t>(*i));
      return;
    }
    if (const auto* u = std::get_if<uint64_t>(&val)) {
      writer.set(tid, col, static_cast<int32_t>(*u));
      return;
    }
  }

  // Fallback: extract as double then coerce to the target type.
  double dval = std::visit(
      [](const auto& v) -> double {
        using T = std::decay_t<decltype(v)>;
        if constexpr (std::is_same_v<T, std::string>) {
          return 0.0;
        } else {
          return static_cast<double>(v);
        }
      },
      val);

  switch (out_kind) {
    case StorageKind::kFloat32:
      writer.set(tid, col, static_cast<float>(dval));
      break;
    case StorageKind::kFloat64: