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Re: Defect Report: Wordings on basic_string::data() disallow small-string optimization

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The original subject was:
Defect Report: Wordings on basic_string::data() disallow small-string
optimization

The last "optimization" was wrapped and dropped from subject for some
reason (80 columns?).


Daniel Kr�gler wrote:
>
> On 2011-08-24 03:56, Kazutoshi Satoda wrote:
>>
>>     void f(std::string&    x, std::string&&    str)
>>     {
>>       char const* const was_pointed = str.data();
>>       x = std::move(str);
>>       assert(x.data() == was_pointed);
>>     }

(snip)
>
> You cannot make normative conclusions from this code, because it invokes
> undefined behaviour. This is so, because the expression
>
> x = std::move(str)
>
> calls a function that (potentially) invalidates the pointer returned
> fromstr.data(), ...

Then, replace the example with this one:

 void f(std::string& x, std::string&& str)
 {
   char const* const was_pointed = str.data();
   x = static_cast<std::string&&>(str);
   assert(x.data() == was_pointed);
 }

>>  I think these wordings of effects on data() are unintentionally
>>  over-constraining, and should be relaxed to keep the rationale for
>>  C.2.11 "Allow small-string optimization" really valid.
>
> I have not yet seen an example which proves this. Your above given
> example is invalid.

I believe the above revised example is now good to show the problem.

--
k_satoda


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Re: Defect Report: Wordings on basic_string::data() disallow small-string optimization Kazutoshi Satoda <k_satoda@f2.dion.ne.jp> - 2011-08-28 08:42 -0700
  Re: Defect Report: Wordings on basic_string::data() disallow small-string optimization Daniel Krügler<daniel.kruegler@googlemail.com> - 2011-08-28 11:06 -0700

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