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Re: [PATCH, c++0x] Use decltype in libstdc++'s parallel/base.h


On Wed, Jun 25, 2008 at 8:32 PM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
> Hi Chris,
>
> you are raising an interesting issue. First blush the code in base.h seems indeed quite hackish and C++ is certainly moving toward good solutions for such kind of problems. My doubts:
>
> 1- Can you describe in a bit of detail the problems you are actually encountering? (seeing a long error message without context doesn't really help, ehm ;)

Right. Sorry about that, here's the snippet:

#include <parallel/algorithm>
#include <parallel/numeric>

template<typename T, std::size_t N>
void parallel_sort_test(std::array<T,N> & data)
{
    __gnu_parallel::sort(data.begin(), data.end());
}

Compiled with something like:
g++ -ftemplate-depth-128 -O0 -fno-inline -Wall --std=c++0x -pthread -fopenmp

It looks like it doesn't recognize "typeof" as a keyword or builtin or
whatever it is. So the expression in base.h is something like
typeof(*static_cast<T*>(NULL) * *static_cast<T*>(NULL)) result;

The first couple of errors are:
expected identifier before '*' token
expected ',' or '...' before 'static_cast'

__typeof__ I think would work. This common_type is interesting
however. Is it going in?

> 2- Johannes opinion?
> 3- Do we believe decltype is sufficiently stable for our uses at least? (comp. e.g., c++/36628)
> 4- Shall we just implement (__)common_type (n2615 -> n2661)?
>
> Opinions?
>
> Thanks,
> Paolo.
>
>


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