[Blitz-support] yet one more auto-return-type / blitz::safeToReturn() question

[Sylwester A. <sa...@ig...>]

Dear Patrik,

On 30/04/12 11:34, Sylwester Arabas wrote:
> On Apr 30, 2012, at 12:47 AM, Patrik Jonsson wrote:
>> I have a hunch -- the array you're generating with B(Range) goes out
>> of scope, so the expression is pointing to an array that no longer
>> exists. There is a way to make the expression hold a *copy* of the
>> Array instead of a reference by using the function safeToReturn(expr).
>> Take a look at the safeToReturn.cpp in the testsuite.
>>
>> Let me know if that helps.
>
> Yes it does!

I'll allow myself to ask yet one more question regarding the C++11 auto 
return type and the blitz::safeToReturn(): why the code below fails on 
F_safe() call while it does work with F() call?

------------------------------------------------------------------------
$ cat test.cpp
#include <blitz/array.h>
using namespace blitz;
using namespace std;

template <class T1, class T2>
auto F(const T1 &a1, const T2 &a2)
-> decltype(a1 * a2)
{ return a1 * a2; }

template <class T1, class T2>
auto F_safe(const T1 &a1, const T2 &a2)
-> decltype(safeToReturn(a1 * a2))
{ return safeToReturn(a1 * a2); }

int main()
{
   Range i(0, 10);
   Array<double,1>
     A(Range(-1, 11)),
     B(Range(-1, 11)),
     C(Range( 0, 11));

   cerr << "F() ..." << endl;
   A(i) = F(B(i), C(i));
   cerr << "F_safe() ..." << endl;
   A(i) = F_safe(B(i), C(i));
}
$ g++ -DBZ_DEBUG -std=c++11 test.cpp -lblitz
$ ./a.out
F() ...
F_safe() ...
/usr/local/include/blitz/bounds.h:71 Two array operands have different
lower bounds: in rank 0, the bounds are -1 and 0

a.out: /usr/local/include/blitz/bounds.h:72: static int 
blitz::bounds::compute_lbound(int, int, int): Assertion `0' failed.
Aborted
------------------------------------------------------------------------

Tested with the current version from the repository.

Thanks,
Sylwester

-- 
http://www.igf.fuw.edu.pl/~slayoo/