The [[nodiscard]] attribute can be placed on type declarations to indicate that any value of such type should not be discarded when
returned from a function. Accompanying the attribute with the message, explaining why values should not be ignored, contributes to a better
understanding of code. This is especially important in the case of types, as the reason for which values of the type should not be discarded is a
defining property of that type (information about failure, handle owning a scarce resource).
Moreover, marking a type as nodiscard, causes a warning to be reported for invocation of every function that returns this type. As a
consequence, the cause of the warning is not directly visible from the declaration of the function and requires further investigation from the
user.
This rule raises an issue when [[nodiscard]] is used on a type without any explanation.
Noncompliant code example
struct [[nodiscard]] status_code { // Noncompliant
int code();
};
status_code open(std::string_view path);
int main()
{
open("/home/user/list.txt"); // warning is raised here
}
Compliant solution
struct [[nodiscard("Possible errors should be checked")]] status_code {
int code();
};
