cython does not find appropriate overloaded constructor

[Lee Zamparo]

I'm trying to compile and run tests of cyrand using cython, but am running into a bizarre compile error when testing overloaded constructors. See this gist for the complete definitions of the files in question.  I'm using python: 2.7.10 (Anaconda 2.0.1) with cython: 0.22.1.

From the gist, I can compile and run example.pyx just fine, which uses the default constructor:

import numpy as np
cimport numpy as np

cimport cython

include "random.pyx"

@cython.boundscheck(False)
def example(n):

    cdef int N = n

    cdef rng r
    cdef rng_sampler[double] * rng_p = new rng_sampler[double](r)
    cdef rng_sampler[double] rng = deref(rng_p)

    cdef np.ndarray[np.double_t, ndim=1] result = np.empty(N, dtype=np.double)

    for i in range(N):
        result[i] = rng.normal(0.0, 2.0)
    print result
    return result

^ this works and runs fine. An example run produces the following output:

$ python test_example.py [ 0.47237842 3.153744849 3.6854932057 ]

Yet when I try to compile and run the test which used a constructor that takes an unsigned long as argument:

import numpy as np
cimport numpy as np

cimport cython

include "random.pyx"

@cython.boundscheck(False)
def example_seed(n, seed):

    cdef int N = n
    cdef unsigned long Seed = seed

    cdef rng r
    cdef rng_sampler[double] * rng_p = new rng_sampler[double](Seed)
    cdef rng_sampler[double] rng = deref(rng_p)

    cdef np.ndarray[np.double_t, ndim=1] result = np.empty(N, dtype=np.double)

    for i in range(N):
        result[i] = rng.normal(0.0, 2.0)
    print result
    return result

I get the following cython compiler error:

    Error compiling Cython file:
    ----------------------------------------------------------- 
    ...    
       cdef int N = n    
       cdef unsigned long Seed = seed

       cdef rng_sampler[double] * rng_p = new rng_sampler[double](Seed)
    ---------------------------------------------------------- 
    example/example_seed.pyx:15:67 Cannot assign type 'unsigned long' to 'mt19937'

I interpret this message, along with the fact that example.pyx compiles and produces a working example.so file, that cython cannot find (or manage) the rng_sampler constructor that takes an unsigned long as input.  Below is the definition of the rng_sampler cppclass: 

import numpy as np
cimport numpy as np
cimport cython

from cython.operator cimport dereference as deref

from libcpp cimport bool

cdef extern from "boost/random/mersenne_twister.hpp" namespace "boost::random" nogil:
    # random number generator
    cdef cppclass mt19937:
        #init
        mt19937() nogil
        #attributes

        #methods
        seed(unsigned long)


cdef extern from "rng_wrapper.hpp" nogil:
    # wrapper to distributions ...
    cdef cppclass rng_sampler[result_type]:
        #init
        rng_sampler(mt19937) nogil         // <- this constructor works fine in the example.pyx test
        rng_sampler(unsigned long) nogil   // <- this constructor is not found in the example_seed.pyx test
        rng_sampler()  nogil               // <- who knows about this one.

        # methods (gamma and exp are using rate param)
        result_type normal(result_type, result_type) nogil
        result_type gamma(result_type, result_type) nogil
        result_type uniform(result_type, result_type) nogil
        result_type exp(result_type) nogil
        result_type chisq(result_type) nogil

ctypedef mt19937 rng

I've not used cython before, and my cpp is middling at best. Can anyone shed light on how to fix this simple problem?

Thanks,

Lee.

[slonik]

This is weird. Can you try explicit cast:

cdef rng_sampler[double] * rng_p = new rng_sampler[double](<unsigned long> 123)

--Leo

[Lee Zamparo]

Explicitly casting the argument to unsigned long as you suggest yields the same compiler error message.  Good suggestion though, thanks.  Could this be a bug?

[slonik]

On Friday, July 31, 2015 at 10:43:07 AM UTC-4, Lee Zamparo wrote:

Explicitly casting the argument to unsigned long as you suggest yields the same compiler error message.  Good suggestion though, thanks.  Could this be a bug?

It does *not* look as a bug to me. The following minimal example shows that cython (both 0.22.1 and git master) resolves overloaded constructors OK.  Compile with:
$ cython -o foo.cc --cplus -2 -f -v foo.pyx

### foo.pyx
cdef extern from *:
    cdef cppclass Bar:
        Bar()

    cdef cppclass Foo[T]:
        Foo()
        Foo(Bar)
        Foo(unsigned long)
        T next()

cdef Bar bar
cdef unsigned int ui= 123
cdef Foo[double] foo0
cdef Foo[double] *p_foo1= new Foo[double](bar)
cdef Foo[double] *p_foo2= new Foo[double](ui)
cdef double x= p_foo2.next()
####

 --Leo

[Lee Zamparo]

Thanks.  I had a comment on my SO post that claims it works using cython 0.21.1.   I've downgraded to 0.21.1 and installed a different version of boost, and now it works.  Thanks for helping me track this down.