c++ - Operator overload which permits capturing with rvalue but not assigning to -

is possible design , how should make overloaded operator+ class c have possible:

c&& c = c1 + c2; 

but not possible:

c1 + c2 = something; 

edit: changed objects small letters. c1, c2 , c objects of class c. && not logical operator&&, rather rvalue reference.

for example writing:

double&& d = 1.0 + 2.0; 

is 100% proper (new) c++ code, while

1.0 + 2.0 = 4.0; 

is compiler error. want exactly same, instead double, class c.

second edit: if operator returns c or c&, can have assignment rvalue reference, assignment c1 + c2, senseless. giving const here disables it, disables assignment rvalue too. @ least on vc++ 2k10. how double this?

have assignment operator callable on lvalues only:

class c {     // ...  public:      c& operator=(const c&) & = default; }; 

note single ampersand after closing parenthesis. prevents assigning rvalues.