[Proposal] Error.what() rvalue move return #504
Description
Motivation:
I have a custom error class which currently has to copy Error::what_ which can get expensive with large error messages.
Possible Solution:
std::string what() && { return std::move(what_); }
Example:
class Error {
public:
Error(const std::string& _what)
: what_(_what) {}
Error(const Error& e) = default;
Error& operator=(const Error&) = default;
/// Returns the error message, equivalent to .what() in std::exception.
const std::string& what() const { return what_; }
/// Only qualifies if Error is a rvalue reference
std::string what() && { return std::move(what_); }
private:
/// Documents what went wrong
std::string what_;
};
struct MyLibError {
std::string message;
//....
};
auto ParseSomething() -> MyLibError {
auto result = Error("Parsing failed"); // rfl error message can become really long if many fields are missing
// making a copy expensive
return MyLibError(std::move(result).what()); // Moved instead of expensive copy
}