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

"Igor Tandetnik" <>
Fri, 14 Dec 2007 08:56:53 -0500
"George" <> wrote in message

Your reply is very helpful. I have performed some further self-study.
In my understanding, rvalue could be in two cases,

1. constant;

2. temporary object (e.g. function return value if the return value
is not a reference -- this is my sample for source() function,

Sounds about right.

Another question is, why currently the compiler does not allow
binding a non-const reference to an rvalue? What is the internal
reason and benefits/risks behind this rule?

To avoid surprises like this:

void f(long& x) { x = 1; }

int y = 0;
f(y); // hypothetical, doesn't compile
assert(y == 1); // fails

If f(y) were allowed to compile, it would generate a temporary of type
long, and the function would modify that temporary, leaving the original
int variable unchanged.

It would also mean that a seemingly benign change in function
signature( from f(int&) to f(long&) ) may silently alter the behavior of
the program. As things stand now, such a change would lead to compiler
errors - much better than silent behavior change.
With best wishes,
    Igor Tandetnik

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