C++ Attributes [[nodiscard]]
Example
C++17
The [[nodiscard]] attribute can be used to indicate that the return value of a function shouldn't be ignored when you do a function call. If the return value is ignored, the compiler should give a warning on this. The attribute can be added to:
- A function definition
- A type
Adding the attribute to a type has the same behaviour as adding the attribute to every single function which returns this type.
template<typename Function>
[[nodiscard]] Finally<std::decay_t<Function>> onExit(Function &&f);
void f(int &i) {
assert(i == 0); // Just to make comments clear!
++i; // i == 1
auto exit1 = onExit([&i]{ --i; }); // Reduce by 1 on exiting f()
++i; // i == 2
onExit([&i]{ --i; }); // BUG: Reducing by 1 directly
// Compiler warning expected
std::cout << i << std::end; // Expected: 2, Real: 1
}
See the proposal for more detailed examples on how [[nodiscard]] can be used.
Note: The implementation details of Finally/onExit are omitted in the example, see Finally/ScopeExit.
