> As far as I can see, none of the assignment operators provided by the
> Standard Library have a ref-qualifier, looking at the latest Draft,
> www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2800.pdf
>
> An ref-qualifier could be helpful to prevent people from accidentally
> assigning to an rvalue, as I understand from Bronek Kozicki and Daveed
> Vandevoorde, www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1821.htm

FYI, the paper on this subject, that I wrote together with Daniel
Kruegler, has just been published, as part of the 2009 pre-Summit mailing:

"Ref-qualifiers for assignment operators of the Standard Library"
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2819.html


Kind regards, Niels

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Niels Dekker
http://www.xs4all.nl/~nd/dekkerware
Scientific programmer at LKEB, Leiden University Medical Center

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As far as I can see, none of the assignment operators provided by the
Standard Library have a ref-qualifier, looking at the latest Draft,
www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2800.pdf

An ref-qualifier could be helpful to prevent people from accidentally
assigning to an rvalue, as I understand from Bronek Kozicki and Daveed
Vandevoorde, www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1821.htm

For example:

 //////////////////////////////////////////////////
 #include <cstdlib>

 struct S {
  S& operator=(S const&) &; // ref-qualifier
  operator bool() const;
 };

 S func();

 int main() {
  S value;
  if ( func() = value )  // Error!  (Typical typo.)
    return EXIT_FAILURE;

  return EXIT_SUCCESS;
 }
 //////////////////////////////////////////////////

Are those ref-qualifiers still to be added to the assignment operators
within the Library?


Kind regards,
--
Niels Dekker
http://www.xs4all.nl/~nd/dekkerware
Scientific programmer at LKEB, Leiden University Medical Center

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On Dec 16, 7:34 am, "Niels Dekker - no return address"
<nore...@this.is.invalid> wrote:
> As far as I can see, none of the assignment operators provided by the
> Standard Library have a ref-qualifier, looking at the latest Draft,www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2800.pdf
>
> An ref-qualifier could be helpful to prevent people from accidentally
> assigning to an rvalue, as I understand from Bronek Kozicki and Daveed
> Vandevoorde,www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1821.htm
>
> For example:
>
>  //////////////////////////////////////////////////
>  #include <cstdlib>
>
>  struct S {
>   S& operator=(S const&) &; // ref-qualifier
>   operator bool() const;
>  };
>
>  S func();
>
>  int main() {
>   S value;
>   if ( func() = value )  // Error!  (Typical typo.)
>     return EXIT_FAILURE;
>
>   return EXIT_SUCCESS;
>  }
>  //////////////////////////////////////////////////
>
> Are those ref-qualifiers still to be added to the assignment operators
> within the Library?

One important use-case for ref-qualifications for basically
all member functions seem to be all atomic types in the
recent library draft. As of

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2514.html

the section "Ambiguity and Insecurity" ends with the sentence:

"In summary, atomic objects are only lvalues, never rvalues."

Just my 2 Euro cents,

Daniel



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