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|  How to Fix Error: no type named 'result_of_t' in namespace 'std'

How to Fix Error: no type named 'result_of_t' in namespace 'std'

October 14, 2024

Resolve the C++ 'no type named result_of_t' error in your firmware development with our clear, concise guide. Boost your coding efficiency effortlessly.

How to Fix Error: no type named 'result_of_t' in namespace 'std'

 

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.

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