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Niels Dekker - no return
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 Posted: Tue Dec 16, 2008 6:34 am Post subject: Ref-qualifiers for assignment operators in the Standard Libr |
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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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Guest
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| Posted: Tue Dec 16, 2008 8:55 pm Post subject: Re: Ref-qualifiers for assignment operators in the Standard |
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On Dec 16, 7:34 am, "Niels Dekker - no return address"
<nore...@this.is.invalid> wrote:
| Quote: | 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
--
[ comp.std.c++ is moderated. To submit articles, try just posting with ]
[ your news-reader. If that fails, use mailto:std-c++@netlab.cs.rpi.edu]
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[ FAQ: http://www.comeaucomputing.com/csc/faq.html ] |
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