Challenge: Callback Function Compatibility Validation

Problem statement

Ensuring that callback functions are type-safe and compatible with a given context is crucial in modern programming. You are tasked to create a utility named CallbackValidator that allows users to check whether a given callable object (such as a function or lambda) is compatible with a set of argument types and a return type. The CallbackValidator should provide a simple and intuitive way to verify if a callback function can be safely called with certain arguments and returns a type that matches expectations.

Note: Your implementation should utilize modern C++20 features, such as requires, concepts, etc., to achieve the required functionality.

Analysis

We can extract the following information from the problem statement:

• The callable_with_args concept: A concept that checks if the argument types of the given function match the callback requirements. For this, we can use the std::invocable concept from the standard concept library.

• The callable_with_return concept: A concept that checks if the return type of the given function matches the callback requirements.

• The CallbackValidator template class: A template class that takes three template parameters:

  • Callable: The callable object

  • Return: The expected return type

  • Args...: The expected argument types

• The validate() function: A function that tells the user about the compatibility of the given function.

Let’s make the problem clearer with the following visual: