[ENH] Possible deduplication of function argument unpacking

[da-woods]

Is your feature request related to a problem? Please describe.

I think there's scope to deduplicate some of the function unpacking code.

e.g.:

def f(a, b, c):
    pass

goes to

PyObject* values[3] = {0,0,0};
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  #if !CYTHON_METH_FASTCALL
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  __pyx_nargs = PyTuple_Size(__pyx_args); if (unlikely(__pyx_nargs < 0)) return NULL;
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  __pyx_kwvalues = __Pyx_KwValues_FASTCALL(__pyx_args, __pyx_nargs);
  {
    PyObject **__pyx_pyargnames[] = {&__pyx_n_s_a,&__pyx_n_s_b,&__pyx_n_s_c,0};
    if (__pyx_kwds) {
      Py_ssize_t kw_args;
      switch (__pyx_nargs) {
        case  3: values[2] = __Pyx_Arg_FASTCALL(__pyx_args, 2);
        CYTHON_FALLTHROUGH;
        case  2: values[1] = __Pyx_Arg_FASTCALL(__pyx_args, 1);
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        case  1: values[0] = __Pyx_Arg_FASTCALL(__pyx_args, 0);
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        case  0: break;
        default: goto __pyx_L5_argtuple_error;
      }
      kw_args = __Pyx_NumKwargs_FASTCALL(__pyx_kwds);
      switch (__pyx_nargs) {
        case  0:
        if (likely((values[0] = __Pyx_GetKwValue_FASTCALL(__pyx_kwds, __pyx_kwvalues, __pyx_n_s_a)) != 0)) {
          (void)__Pyx_Arg_NewRef_FASTCALL(values[0]);
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        else if (unlikely(PyErr_Occurred())) __PYX_ERR(0, 3, __pyx_L3_error)
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        CYTHON_FALLTHROUGH;
        case  1:
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        CYTHON_FALLTHROUGH;
        case  2:
        if (likely((values[2] = __Pyx_GetKwValue_FASTCALL(__pyx_kwds, __pyx_kwvalues, __pyx_n_s_c)) != 0)) {
          (void)__Pyx_Arg_NewRef_FASTCALL(values[2]);
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        else if (unlikely(PyErr_Occurred())) __PYX_ERR(0, 3, __pyx_L3_error)
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    } else if (unlikely(__pyx_nargs != 3)) {
      goto __pyx_L5_argtuple_error;
    } else {
      values[0] = __Pyx_Arg_FASTCALL(__pyx_args, 0);
      values[1] = __Pyx_Arg_FASTCALL(__pyx_args, 1);
      values[2] = __Pyx_Arg_FASTCALL(__pyx_args, 2);
    }

Much of this is shared between every three argument function. Essentially the only bit that isn't dictated by the function signature is the keyword name (and those could be passed in as an argument).

Describe the solution you'd like.

My view is that the signature (i.e. types and numbers of arguments) dictates most of the logic here, and names and any default values dictates the rest of the logic.

It'd therefore be possible to factor out a large amount of code from functions with the same signature (which could be inlined/not inlined as desired).

I wouldn't propose to go for something completely generic that handles any number of arguments - I think it's reasonable to generate optimized and specific code, but it may as well be shared in cases where it's genuinely identical.

Describe alternatives you've considered.

No response

Additional context

No response