[mlpack] Question about Armadillo

[Kirill Mishchenko]

The type of T is 

arma::Glue<arma::Op<arma::Gen<arma::Col<double>, arma::gen_zeros>, arma::op_htrans>, arma::Op<arma::Gen<arma::Col<double>, arma::gen_zeros>, arma::op_htrans>, arma::glue_join_rows>

I guess there should be something wrong with the line 

const T& ref = arma::join_rows(arma::zeros(2).t(), arma::zeros(2).t());

since this works fine

template<typename T>
void f(const T& arg)
{
  arma::mat m = arg;
}

BOOST_AUTO_TEST_CASE(RefTest)
{
  f(arma::join_rows(arma::zeros(2).t(), arma::zeros(2).t()));
}

Best regards,

Kirill Mishchenko



> On 27 Jun 2017, at 20:35, Ryan Curtin <ryan at ratml.org> wrote:
> 
> On Tue, Jun 27, 2017 at 08:28:00PM +0500, Kirill Mishchenko wrote:
>>> I believe this is a result of strange inference by the compiler.  You
>>> should double-check my explanation here, I'm not 100% sure that it is
>>> correct, but my gut feeling is that it is…
>> 
>> It looks like there is some other reason. I got the same error when I tried the following
>> 
>> template<typename T>
>> void g(const T&)
>> {
>>  const T& ref = arma::join_rows(arma::zeros(2).t(), arma::zeros(2).t());
>>  arma::mat m = ref;
>> }
>> 
>> BOOST_AUTO_TEST_CASE(RefTest4)
>> {
>>  g(arma::join_rows(arma::zeros(2).t(), arma::zeros(2).t()));
>> }
> 
> I think this is the same thing, the compiler deduces a strange type for
> T.  Also, sometimes Armadillo can give better output when compiled in
> debugging mode (so I guess reconfigure CMake with -DDEBUG=ON), that may
> provide a better output for diagnosis than just a segfault.
> 
> I am curious, do you know what the deduced type for T is?  That may shed
> additional light on the failure.
> 
> -- 
> Ryan Curtin    | "Wha' happened?"
> ryan at ratml.org <mailto:ryan at ratml.org> |   - Mike LaFontaine

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