Re: How to assign a non-const object to const reference

Alamelu <Alamelu@discussions.microsoft.com> wrote:


You are confusing two completely distinct situations: binding a
reference to an object, and assigning to an already-bound reference
(which is equivalent to assigning to an underlying object).

A reference must be bound to an object when it is created. Once bound,
it cannot be re-bound to a different object (aka reseated) - it becomes
an alias to an original object.

With this in mind, consider:

void DerivedClass::Get (const AClass &refA)
{
    refA = m_objA;
}
const AClass objA;
derived.Get(objA);

At the point of invocation of Get(), a reference refA is bound to the
function argument objA, and becomes just another name for this object. A
statement in the body of the function is effectively equivalent to objA
= m_objA, which is illegal since objA is const.

const AClass& DerivedClass::Get()
{
    return m_ObjA;
}

Here, the reference is a return value. A reference is created only when
the function returns, and is bound to the return value of the function.
No assignment takes place here: the function produces an (unnamed)
reference bound to m_ObjA. An assignment, if any, must take place
outside the function, at the call site. And of course, if the caller
does something like this

const AClass objA;
objA = derived.Get();

they'll get the same error as in the first case.
--
With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925