c++ - 在protobuf中，copyFrom优先于赋值吗？

Question

以下代码将在运行时失败:

auto cell = addFilterCell(m_filterSlot, idx, odx, section_idx, 48000);
if(request->has_iir()) {
    auto filter = cell->mutable_iir();
    filter->CopyFrom(request->iir());
} else if(request->has_fir()) {
    auto filter = cell->mutable_fir();
    filter->CopyFrom(request->iir()); // Runtime failure

因为我尝试将 IIR 消息复制到 FIR 消息中。 但如果我使用赋值，错误的代码将在编译时失败:

if(request->has_iir()) {
    auto filter = cell->mutable_iir();
    *filter = request->iir();
} else if(request->has_fir()) {
    auto filter = cell->mutable_fir();
    *filter = request->iir();  //compile time error

但是，我看到很多 copyFrom 使用情况，值得鼓励 here 。 从我的角度来看，在上述情况下，使用赋值更安全。 使用赋值可能有哪些缺点？

根据这段生成的代码，在内部，赋值运算符是 copyFrom 的包装器。

class FilterCell : public ::google::protobuf::Message /* @@protoc_insertion_point(class_definition:dio.endpoint.FilterCell) */ {
 public:
  FilterCell();
  virtual ~FilterCell();

  FilterCell(const FilterCell& from);

  inline FilterCell& operator=(const FilterCell& from) {
    CopyFrom(from);
    return *this;
  }

Answer 1

您问题的答案在 the link you provided .

"The assignment operator simply wraps CopyFrom, so the behavior is exactly the same. Stylistically we prefer to use CopyFrom over =, because it can be an expensive operation and = makes it look deceptively simple. The operator= overload primarily exists for compatibility with STL, but of course you're free to use it as you choose."

^强调我的

它表示赋值运算符已重载，并且简单地包装了 copyFrom() 函数。因此两者之间没有行为差异。