TODO

# TODO

## Automatic generation of the .pxd file?

  xdress maybe? did not manage to install: complaining when trying to
  link against clang libraries that are provided as static libraries.

## Automatic generation of the Python wrappers?

## Fetch features from Sage's experimental interface to Semigroupe

  https://trac.sagemath.org/attachment/ticket/8360/trac_8360_semigroupe-interface-nt.patch

## Use pos_t rather than size_t everywhere relevant

Problem: pos_t is a private typedef in the Semigroup class; this makes
it harder to use it elsewhere

## new_from_handle would naturally be a class method

Question: how to achieve this in Cython?

## libsemigroups configuration

- DEFAULT_REPORT_VALUE : is there a gain in making it a const?
- DEFAULT_NR_THREADS : make a new default value? or an attribute of the semigroup?

## Fix memory management

Problem: when we get back a pointer to an Element from libsemigroup;
when shall we consider that we own it or not?

At this stage when semigroups.pyx returns a wrapper around a
libsemigroup element, it is always assumed that libsemigroup owns that
element. Which is wrong when the element is part of the internal data
structure for the semigroup. This quickly leads to segmentation faults
with the following backtrace:

    #1  0x00007ffef6343ef3 in __pyx_pf_10semigroups_7Element_2__dealloc__ (__pyx_v_self=0x7ffff011baf0) at semigroups.cpp:1382
    #2  __pyx_pw_10semigroups_7Element_3__dealloc__ (__pyx_v_self=) at semigroups.cpp:1354
    #3  __pyx_tp_dealloc_10semigroups_Element (o=) at semigroups.cpp:3240
    #4  0x00007ffff7a44711 in list_dealloc (op=) at Objects/listobject.c:309
    #5  0x00007ffff7a56c13 in PyDict_Clear (op=<optimized out>) at Objects/dictobject.c:946
    #6  0x00007ffff7a56c99 in dict_clear (mp=<optimized out>) at Objects/dictobject.c:2028
    #7  0x00007ffff7ac9ef2 in call_function (oparg=<optimized out>, pp_stack=0x7fffffffc370) at Python/ceval.c:4336

How to fix this?

Plausibly, we should

- have a parameter in new_from_handle to decide whether the instance
  owns the handle or is just a view on it.

- review all methods of Semigroup, and call new_from_handle appropriately