C++17 std::optional Not Propagating Errors in Custom Class with Move Semantics
I'm converting an old project and I'm testing a new approach and Does anyone know how to I'm working on a project and hit a roadblock. I'm working with an scenario with using `std::optional` in conjunction with a custom class that implements move semantics. I have a class `MyResource` that manages some resources, and I want to return an `std::optional<MyResource>` from a factory function. However, I'm working with unexpected behavior when the resource allocation fails. My factory function is supposed to return an empty `std::optional` when it fails, but instead, I'm seeing an unhandled exception thrown during the move operation. Here's a simplified version of my code: ```cpp #include <iostream> #include <optional> #include <stdexcept> class MyResource { public: MyResource() { // Simulate resource allocation if (/* some condition */) { throw std::runtime_error("Failed to allocate resource"); } std::cout << "Resource allocated" << std::endl; } MyResource(MyResource&& other) noexcept { // Move logic std::cout << "Resource moved" << std::endl; } ~MyResource() { std::cout << "Resource destroyed" << std::endl; } }; std::optional<MyResource> CreateResource() { try { MyResource res; return res; // This line causes the scenario } catch (const std::exception& e) { std::cerr << e.what() << std::endl; return std::nullopt; } } int main() { auto resource = CreateResource(); if (!resource) { std::cerr << "Resource creation failed" << std::endl; } return 0; } ``` The behavior message I receive is not quite clear, but it seems to point to the copy/move constructor being invoked when I attempt to return `res`. I thought that since I'm returning an `std::optional`, it would handle the move for me without throwing an exception when the resource couldn't be allocated. What am I missing here? Should I be using a different approach to ensure that the factory function behaves as expected? Any insights would be appreciated. For context: I'm using Cpp on Linux. What are your experiences with this? This is happening in both development and production on CentOS. Any ideas how to fix this? I'm using Cpp 3.11 in this project. I appreciate any insights! I'm developing on CentOS with Cpp. Is there a better approach?