DEFINITION 2: ATTRIBUTES PROPERTIES - PRATMG/2143-OOP-Tamang GitHub Wiki

Attributes are a key feature of modern C++ that allow the programmer to provide additional information to the compiler in order for it to enforce constraints (conditions), optimize specific pieces of code, or generate specific code. In basic terms, an attribute serves as an annotation or a note to the compiler, providing additional information about the code for optimization and enforcing certain conditions on it. 

#include <iostream>

// Not implemented by compilers as of now
// but will be implemented in the future
[[nodiscard]] int f(int i)[[expects:i > 0]]
{
	std::cout << " Always greater than 0!"
			<< " and return val must "
			<< "always be utilized";
}

My reference:

• https://www.geeksforgeeks.org/attributes-in-c/