Re: More keyword abomination by C++0x

Thu, 30 Apr 2009 18:22:20 CST
On Apr 30, 12:39 pm, "Chris Morley" <> wrote:

Newbie's questions would just be different. There would be _no_ posts about
const references to temporaries and references as l-values and r-values or
std::swap ;o)

Yes, there would. Take for example the following program using your
rules for operator overloading.

     struct foo_t
     { foo_t* operator+= (int* y) { *y = 3; }
     int main()
     { foo_t f;
         long z = 2;
         f += z;
         return z;

The problem is implicit conversions. Implicit conversions are why we
have questions about binding a non-const ref to a temporary.

The only reasonable option I see for the above program is don't
compile. You are trying to bind a non-const reference (or pointer in
this case) to the result of an implicit conversion from long to int, a
temporary. The alternative would be to allow writing to the temporary,
but the above program would return 2, not 3, and we would instead get
a lot of questions on that, and a lot of hassle from competent
programmers about implicit conversions being the devil. (I suppose an
alternative would be to outlaw all implicit conversions, but I think
that's going quite overboard.)

References are a red herring. The real problem is implicit conversions
in function arguments creating temporaries, implicitly aka without any
source code to do the conversion, and this may surprise people if
they're allowed to modify that temporary in the function but the
temporary is immediately destroyed, leaving the source of the implicit
conversion unchanged.

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