The name *real-if-needed* denotes an exposition-only function object.

The expression *real-if-needed*(E) for a subexpression E
whose type is T is expression-equivalent to:

- real(E),
if T is not an arithmetic type and
the expression real(E) is valid,
with overload resolution performed in a context that includes the declaration
template<class T> T real(const T&) = delete;
If the function selected by overload resolution does not return the real part of its input, the program is ill-formed, no diagnostic required;
- otherwise, E.