Understanding the Issue
- The error "no type named 'result_of_t' in namespace 'std'" suggests that your code is trying to utilize `std::result_of_t`, which has been deprecated in C++17 and removed in C++20.
- The probable cause of this error is that the code is using APIs or constructs that rely on the obsolete `std::result_of_t` type trait.
- The solution involves updating the code to be compatible with the newer C++ standards. This typically means replacing `std::result_of_t` with its successor, `std::invoke_result_t`.
Replace with std::invoke_result_t
- Identify where `result_of_t` is used in your code. These will typically appear in template-based code.
- Replace `std::result_of_t` with `std::invoke_result_t`. The `std::invoke_result_t` provides a way to get the return type of a callable when invoked with specified argument types.
// Before
std::result_of_t<F(Args...)> result = someFunction(args...);
// After
std::invoke_result_t<F, Args...> result = someFunction(args...);
Understand std::invoke_result_t
- `std::invoke_result_t` uses the `std::invoke` mechanism under the hood, which allows it to work uniformly for pointers to member functions, pointers to data members, and other callable entities such as lambdas or function objects.
- This approach not only makes code future-proof by aligning with C++20 standards but also enhances overall code flexibility and compatibility.
Ensure Compiler Compatibility
- Verify that your compiler supports C++17 or C++20, as these standards provide `std::invoke_result_t`. This can usually be done by setting the appropriate standard flag, like `-std=c++17` or `-std=c++20` when compiling your code.
- If you're working within a constrained embedded environment requiring C++14, consider manually backporting a solution or refactoring the involved code to avoid complex traits.
Check Third-Party Libraries
- If your project depends on third-party libraries, those might still use `std::result_of_t`. Ensure these are updated to recent versions compatible with C++17/C++20 standards.
- If updates are not available, you may need to modify the library code (following any license agreements) or decide on alternative libraries.
Test the Updated Code
- After making these changes, thoroughly test your firmware to verify that the logical behavior of your application remains intact and ensure there are no side effects from replacing `std::result_of_t` with `std::invoke_result_t`.
By conducting these enhancements, you will not only resolve the error but also align the codebase with modern C++ standards, improving its maintainability and compatibility with future updates.
