Way to handle integer template types

[csd]

Hi all,

I am currently trying to wrap a C++ template class in Cython representing a sparse matrix. Here is a snippet of the C++ code:

template <class T, int S=Eigen::ColMajor>
class SparseMatrixExt:public SparseMatrix<T, S> {
...

Basically T is the data type of the elements of the matrix (int, float etc.) and S is an integer which dictates how entries are stored. When I try to wrap this in Cython I get the error "unknown type in template argument" referring to a fixed value of S. As far as I know, int template types are not yet supported, but what is the best way around this issue?

Thanks in advance,
Charanpal

[Robert Bradshaw]

You can do

cdef extern from *:
ctypedef void* int_parameter
int_parameter one "1"
int_parameter two "2"
int_parameter three "3"

cdef SparseMatrixExt<double, two> *m = new SparseMatrixExt<double, two>()

- Robert

[Henry Schreiner]

Are there any plans to add support for integer templates to cython? I'd like to have a general wrapper for std::array (would help with std::tuple, too).

[Robert Bradshaw]

On Thu, Apr 3, 2014 at 11:03 AM, Henry Schreiner
<henrysch...@gmail.com> wrote:
> Are there any plans to add support for integer templates to cython? I'd like
> to have a general wrapper for std::array (would help with std::tuple, too).

Not at the moment, though I can see how it would be useful. A
straw-man syntax could be something like CppClass[T, U, int N]?

> On Saturday, March 16, 2013 11:50:00 AM UTC-5, Robert Bradshaw wrote:
>>
>> On Sat, Mar 16, 2013 at 3:56 AM, csd <char...@gmail.com> wrote:
>> > Hi all,
>> >
>> > I am currently trying to wrap a C++ template class in Cython
>> > representing a
>> > sparse matrix. Here is a snippet of the C++ code:
>> >
>> > template <class T, int S=Eigen::ColMajor>
>> > class SparseMatrixExt:public SparseMatrix<T, S> {
>> > ...
>> >
>> > Basically T is the data type of the elements of the matrix (int, float
>> > etc.)
>> > and S is an integer which dictates how entries are stored. When I try to
>> > wrap this in Cython I get the error "unknown type in template argument"
>> > referring to a fixed value of S. As far as I know, int template types
>> > are
>> > not yet supported, but what is the best way around this issue?
>>
>> You can do
>>
>> cdef extern from *:
>> ctypedef void* int_parameter
>> int_parameter one "1"
>> int_parameter two "2"
>> int_parameter three "3"
>>
>> cdef SparseMatrixExt<double, two> *m = new SparseMatrixExt<double, two>()
>>
>> - Robert
>

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[Henry Schreiner]

Or CppClass[T, U, const int N]...

[Moritz Kassner]

+1 on this.

wrapping libs that use Eigen would be so much more elegant with integer templates.

[slonik]

+1 as well! Proper C++ template support would be a huge help for those of us who are using Cython with modern C++ libraries.

--Leo

 

[Robert Bradshaw]

Are you thinking of something like
https://github.com/cython/cython/pull/426 ? It still needs a bit of
work, but if you want this feature sooner you're welcome to help
review it yourself.

- Robert

[Moritz Kassner]

I d love to contribute back to the project which I use a lot a really appreciate! 

As a cython user I don't think I know enough to give useful review feedback :-(. 

Any other way to contribute and see this PR happen?