Re: A non-const reference may only be bound to an lvalue?

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.language

Date:

Sat, 15 Dec 2007 11:08:39 -0500

Message-ID:

<uXLbETzPIHA.5160@TK2MSFTNGP05.phx.gbl>

"George" <George@discussions.microsoft.com> wrote in message
news:B58BC723-F8FC-4EB4-99EA-74294E4C3272@microsoft.com

I do not quite understand why the following code can convert rvalue to
lvalue, could you provide more description please?

template<typename T>
inline T&
lvalue_cast(const T& rvalue)
{
return const_cast<T&>(rvalue);
}

It doesn't really convert anything, it just tricks the compiler into
forgetting that the original object was a temporary.

The compiler sees a function call taking a const reference: a temporary
can be bound to such a parameter. The compiler further sees the function
return a non-const reference: such a return value is an lvalue under C++
rules. The compiler doesn't trace through the body of the function to
determine that the parameter and the result actually refer to the same
object.
--
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