How can you modify an object without calling member functions?

Question

At 3.10/10, the standard says:

An lvalue for an object is necessary in order to modify the object except that an rvalue of class type can also be used to

Answer 1

How can one modify an object [that's specified by an rvalue expression] without calling a member function?

I know of only one way to do that, namely to bind the object to a reference to const, and then cast away the const-ness.

E.g.

template< class Type >
Type& tempRef( Type const& o ) { return const_cast< Type& >( o ); }

struct S { int x; };

int main()
{ tempRef( S() ).x = 3; }

This is because a temporary object is not const itself unless it is of const type, so the example above does not cast away original const-ness (which would be UB).

EDIT, added: Luc Danton’s answer showed another (non-general) way, namely where the temporary's construction stores some reference or pointer to the object in some accessible location.

Cheers & hth.,