[cfe-dev] Looks lie a bug: no implicit conversion from slice_array to valarray in 3.4.1 + libcpp

[Lev Serebryakov]

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On 15.09.2014 20:38, Marshall Clow wrote:

>> I'm using clang 3.4.1 (FreeBSD-CURRENT system compiler) with I'm
>> compile very simple program, which uses <valarray>. Of course, it
>> is test case, I found this bug when try to compile qucs project
>> on this system ============ test.cpp #include <valarray>
>> 
>> int main(int argc, char *argv[]) { std::valarray<double> a(4,
>> 10); std::valarray<double> b(4, 20); a *= b[std::slice(1,1,1)]; 
>> return 0; } =====================
> 
> I’ve opened issue http://llvm.org/bugs/show_bug.cgi?id=20946 to
> track this.
> 
> I’m not sure if this is a bug in libc++, or an extension in
> libstdc++. A quick look at the standard doesn’t show any implicit
> conversions from a single-element slice array (the result of
> 'b[std::slice(1,1,1)]’) to a double.
> 
> Thanks for the report.
 I could be wrong (I'm not C++ guru), but looks like
slice_array<double> should be converted to valarray<double> in such
case with appropriate valarray's constructor (it isn't marked as
"explicit"), because there are appropriate "operator *=" in valarray
class to multiple two valarrays.

 I want to note, that in real code I encounter this, slice was not
single-element, and it worked in gcc 4.8. Maybe, my trimmed example is
not very good (due to single-element slice, which could lead to
confusion).

- -- 
// Lev Serebryakov
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